diff --git a/app/src/androidTest/java/fr/free/nrw/commons/ReviewDaoTest.java b/app/src/androidTest/java/fr/free/nrw/commons/ReviewDaoTest.java
deleted file mode 100644
index f485d5152..000000000
--- a/app/src/androidTest/java/fr/free/nrw/commons/ReviewDaoTest.java
+++ /dev/null
@@ -1,74 +0,0 @@
-package fr.free.nrw.commons;
-
-import static org.hamcrest.CoreMatchers.equalTo;
-import static org.hamcrest.MatcherAssert.assertThat;
-
-import android.content.Context;
-import androidx.room.Room;
-import androidx.test.core.app.ApplicationProvider;
-import androidx.test.ext.junit.runners.AndroidJUnit4;
-import fr.free.nrw.commons.db.AppDatabase;
-import fr.free.nrw.commons.review.ReviewDao;
-import fr.free.nrw.commons.review.ReviewEntity;
-import org.junit.After;
-import org.junit.Before;
-import org.junit.Test;
-import org.junit.runner.RunWith;
-
-@RunWith(AndroidJUnit4.class)
-public class ReviewDaoTest {
-
-    private ReviewDao reviewDao;
-    private AppDatabase database;
-
-    /**
-     * Set up the application database
-     */
-    @Before
-    public void createDb() {
-        Context context = ApplicationProvider.getApplicationContext();
-        database = Room.inMemoryDatabaseBuilder(
-                context, AppDatabase.class)
-            .allowMainThreadQueries()
-            .build();
-        reviewDao = database.ReviewDao();
-    }
-
-    /**
-     * Close the database
-     */
-    @After
-    public void closeDb() {
-        database.close();
-    }
-
-    /**
-     * Test insertion
-     * Also checks isReviewedAlready():
-     * Case 1: When image has been reviewed/skipped by the user
-     */
-    @Test
-    public void insert() {
-        // Insert data
-        String imageId = "1234";
-        ReviewEntity reviewEntity = new ReviewEntity(imageId);
-        reviewDao.insert(reviewEntity);
-
-        // Check insertion
-        // Covers the case where the image exists in the database
-        // And isReviewedAlready() returns true
-        Boolean isInserted = reviewDao.isReviewedAlready(imageId);
-        assertThat(isInserted, equalTo(true));
-    }
-
-    /**
-     * Test review status of the image
-     * Case 2: When image has not been reviewed/skipped
-     */
-    @Test
-    public void isReviewedAlready(){
-        String imageId = "5856";
-        Boolean isInserted = reviewDao.isReviewedAlready(imageId);
-        assertThat(isInserted, equalTo(false));
-    }
-}
\ No newline at end of file
diff --git a/app/src/main/java/fr/free/nrw/commons/mwapi/UserClient.java b/app/src/main/java/fr/free/nrw/commons/mwapi/UserClient.java
deleted file mode 100644
index 8b5cfa72a..000000000
--- a/app/src/main/java/fr/free/nrw/commons/mwapi/UserClient.java
+++ /dev/null
@@ -1,46 +0,0 @@
-package fr.free.nrw.commons.mwapi;
-
-import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse;
-import fr.free.nrw.commons.wikidata.mwapi.MwQueryResult;
-import fr.free.nrw.commons.wikidata.mwapi.UserInfo;
-import fr.free.nrw.commons.utils.DateUtil;
-
-import java.util.Collections;
-import java.util.Date;
-
-import javax.inject.Inject;
-
-import io.reactivex.Observable;
-import io.reactivex.Single;
-
-public class UserClient {
-    private final UserInterface userInterface;
-
-    @Inject
-    public UserClient(UserInterface userInterface) {
-        this.userInterface = userInterface;
-    }
-
-    /**
-     * Checks to see if a user is currently blocked from Commons
-     *
-     * @return whether or not the user is blocked from Commons
-     */
-    public Single<Boolean> isUserBlockedFromCommons() {
-        return userInterface.getUserBlockInfo()
-                .map(MwQueryResponse::query)
-                .map(MwQueryResult::userInfo)
-                .map(UserInfo::blockexpiry)
-                .map(blockExpiry -> {
-                    if (blockExpiry.isEmpty())
-                        return false;
-                    else if ("infinite".equals(blockExpiry))
-                        return true;
-                    else {
-                        Date endDate = DateUtil.iso8601DateParse(blockExpiry);
-                        Date current = new Date();
-                        return endDate.after(current);
-                    }
-                }).single(false);
-    }
-}
diff --git a/app/src/main/java/fr/free/nrw/commons/mwapi/UserClient.kt b/app/src/main/java/fr/free/nrw/commons/mwapi/UserClient.kt
new file mode 100644
index 000000000..b6e3b873b
--- /dev/null
+++ b/app/src/main/java/fr/free/nrw/commons/mwapi/UserClient.kt
@@ -0,0 +1,36 @@
+package fr.free.nrw.commons.mwapi
+
+import fr.free.nrw.commons.utils.DateUtil
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResult
+import fr.free.nrw.commons.wikidata.mwapi.UserInfo
+import io.reactivex.Single
+import java.text.ParseException
+import java.util.Date
+import javax.inject.Inject
+
+class UserClient @Inject constructor(private val userInterface: UserInterface) {
+    /**
+     * Checks to see if a user is currently blocked from Commons
+     *
+     * @return whether or not the user is blocked from Commons
+     */
+    fun isUserBlockedFromCommons(): Single<Boolean> =
+        userInterface.getUserBlockInfo()
+            .map(::processBlockExpiry)
+            .single(false)
+
+    @Throws(ParseException::class)
+    private fun processBlockExpiry(response: MwQueryResponse): Boolean {
+        val blockExpiry = response.query()?.userInfo()?.blockexpiry()
+        return when {
+            blockExpiry.isNullOrEmpty() -> false
+            "infinite" == blockExpiry -> true
+            else -> {
+                val endDate = DateUtil.iso8601DateParse(blockExpiry)
+                val current = Date()
+                endDate.after(current)
+            }
+        }
+    }
+}
diff --git a/app/src/main/java/fr/free/nrw/commons/review/ReviewHelper.java b/app/src/main/java/fr/free/nrw/commons/review/ReviewHelper.java
deleted file mode 100644
index 4119a1751..000000000
--- a/app/src/main/java/fr/free/nrw/commons/review/ReviewHelper.java
+++ /dev/null
@@ -1,166 +0,0 @@
-package fr.free.nrw.commons.review;
-
-
-import androidx.annotation.VisibleForTesting;
-import fr.free.nrw.commons.Media;
-import fr.free.nrw.commons.media.MediaClient;
-import io.reactivex.Completable;
-import io.reactivex.Observable;
-import io.reactivex.Single;
-import io.reactivex.android.schedulers.AndroidSchedulers;
-import io.reactivex.schedulers.Schedulers;
-import java.util.Collections;
-import javax.inject.Inject;
-import javax.inject.Singleton;
-import org.apache.commons.lang3.StringUtils;
-import fr.free.nrw.commons.wikidata.mwapi.MwQueryPage;
-import timber.log.Timber;
-
-@Singleton
-public class ReviewHelper {
-
-    private static final String[] imageExtensions = new String[]{".jpg", ".jpeg", ".png"};
-
-    private final MediaClient mediaClient;
-    private final ReviewInterface reviewInterface;
-
-    @Inject
-    ReviewDao dao;
-
-    @Inject
-    public ReviewHelper(MediaClient mediaClient, ReviewInterface reviewInterface) {
-        this.mediaClient = mediaClient;
-        this.reviewInterface = reviewInterface;
-    }
-
-    /**
-     * Fetches recent changes from MediaWiki API
-     * Calls the API to get the latest 50 changes
-     * When more results are available, the query gets continued beyond this range
-     *
-     * @return
-     */
-    private Observable<MwQueryPage> getRecentChanges() {
-        return reviewInterface.getRecentChanges()
-                .map(mwQueryResponse -> mwQueryResponse.query().pages())
-                .map(recentChanges -> {
-                    Collections.shuffle(recentChanges);
-                    return recentChanges;
-                })
-                .flatMapIterable(changes -> changes)
-                .filter(recentChange -> isChangeReviewable(recentChange));
-    }
-
-    /**
-     * Gets a random file change for review.
-     * - Picks a random file from those changes
-     * - Checks if the file is nominated for deletion
-     * - Retries upto 5 times for getting a file which is not nominated for deletion
-     *
-     * @return Random file change
-     */
-    public Single<Media> getRandomMedia() {
-        return getRecentChanges()
-                .flatMapSingle(change -> getRandomMediaFromRecentChange(change))
-                .filter(media -> !StringUtils.isBlank(media.getFilename())
-                   && !getReviewStatus(media.getPageId())    // Check if the image has already been shown to the user
-                )
-                .firstOrError();
-    }
-
-    /**
-     * Returns a proper Media object if the file is not already nominated for deletion
-     * Else it returns an empty Media object
-     *
-     * @param recentChange
-     * @return
-     */
-    private Single<Media> getRandomMediaFromRecentChange(MwQueryPage recentChange) {
-        return Single.just(recentChange)
-                .flatMap(change -> mediaClient.checkPageExistsUsingTitle("Commons:Deletion_requests/" + change.title()))
-                .flatMap(isDeleted -> {
-                    if (isDeleted) {
-                        return Single.error(new Exception(recentChange.title() + " is deleted"));
-                    }
-                    return mediaClient.getMedia(recentChange.title());
-                });
-
-    }
-
-    /**
-     * Checks if the image exists in the reviewed images entity
-     *
-     * @param image
-     * @return
-     */
-    @VisibleForTesting
-    Boolean getReviewStatus(String image){
-        if(dao == null){
-            return false;
-        }
-        return Observable.fromCallable(()-> dao.isReviewedAlready(image))
-                .subscribeOn(Schedulers.io())
-                .observeOn(AndroidSchedulers.mainThread()).blockingSingle();
-    }
-
-    /**
-     * Gets the first revision of the file from filename
-     *
-     * @param filename
-     * @return
-     */
-    public Observable<MwQueryPage.Revision> getFirstRevisionOfFile(String filename) {
-        return reviewInterface.getFirstRevisionOfFile(filename)
-                .map(response -> response.query().firstPage().revisions().get(0));
-    }
-
-    /**
-     * Checks Whether Given File is used in any Wiki page or not
-     * by calling api for given file
-     *
-     * @param filename
-     * @return
-     */
-     Observable<Boolean> checkFileUsage(final String filename) {
-         return reviewInterface.getGlobalUsageInfo(filename)
-             .map(mwQueryResponse -> mwQueryResponse.query().firstPage()
-                 .checkWhetherFileIsUsedInWikis());
-     }
-
-    /**
-     * Checks if the change is reviewable or not.
-     * - checks the type and revisionId of the change
-     * - checks supported image extensions
-     *
-     * @param recentChange
-     * @return
-     */
-    private boolean isChangeReviewable(MwQueryPage recentChange) {
-        for (String extension : imageExtensions) {
-            if (recentChange.title().endsWith(extension)) {
-                return true;
-            }
-        }
-
-        return false;
-    }
-
-    /**
-     * Adds reviewed/skipped images to the database
-     *
-     * @param imageId
-     */
-    public void addViewedImagesToDB(String imageId) {
-        Completable.fromAction(() -> dao.insert(new ReviewEntity(imageId)))
-            .subscribeOn(Schedulers.io())
-            .observeOn(AndroidSchedulers.mainThread())
-            .subscribe(() -> {
-                // Inserted successfully
-                Timber.i("Image inserted successfully.");
-                },
-                throwable -> {
-                    Timber.e("Image not inserted into the reviewed images database");
-                }
-            );
-    }
-}
diff --git a/app/src/main/java/fr/free/nrw/commons/review/ReviewHelper.kt b/app/src/main/java/fr/free/nrw/commons/review/ReviewHelper.kt
new file mode 100644
index 000000000..16b8d26de
--- /dev/null
+++ b/app/src/main/java/fr/free/nrw/commons/review/ReviewHelper.kt
@@ -0,0 +1,138 @@
+package fr.free.nrw.commons.review
+
+import androidx.annotation.VisibleForTesting
+import fr.free.nrw.commons.Media
+import fr.free.nrw.commons.media.MediaClient
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryPage
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryPage.Revision
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
+import io.reactivex.Completable
+import io.reactivex.Observable
+import io.reactivex.Single
+import io.reactivex.android.schedulers.AndroidSchedulers
+import io.reactivex.schedulers.Schedulers
+import org.apache.commons.lang3.StringUtils
+import timber.log.Timber
+import java.util.Collections
+import javax.inject.Inject
+import javax.inject.Singleton
+
+@Singleton
+class ReviewHelper @Inject constructor(
+    private val mediaClient: MediaClient,
+    private val reviewInterface: ReviewInterface
+) {
+    @JvmField @Inject var dao: ReviewDao? = null
+
+    /**
+     * Fetches recent changes from MediaWiki API
+     * Calls the API to get the latest 50 changes
+     * When more results are available, the query gets continued beyond this range
+     *
+     * @return
+     */
+    private fun getRecentChanges() = reviewInterface.getRecentChanges()
+        .map { it.query()?.pages() }
+        .map(MutableList<MwQueryPage>::shuffled)
+        .flatMapIterable { changes: List<MwQueryPage>? -> changes }
+        .filter { isChangeReviewable(it) }
+
+    /**
+     * Gets a random file change for review.  Checks if the image has already been shown to the user
+     * - Picks a random file from those changes
+     * - Checks if the file is nominated for deletion
+     * - Retries upto 5 times for getting a file which is not nominated for deletion
+     *
+     * @return Random file change
+     */
+    fun getRandomMedia(): Single<Media> = getRecentChanges()
+        .flatMapSingle(::getRandomMediaFromRecentChange)
+        .filter { !it.filename.isNullOrBlank() && !getReviewStatus(it.pageId) }
+        .firstOrError()
+
+    /**
+     * Returns a proper Media object if the file is not already nominated for deletion
+     * Else it returns an empty Media object
+     *
+     * @param recentChange
+     * @return
+     */
+    private fun getRandomMediaFromRecentChange(recentChange: MwQueryPage) =
+        Single.just(recentChange)
+            .flatMap { mediaClient.checkPageExistsUsingTitle("Commons:Deletion_requests/${it.title()}") }
+            .flatMap {
+                if (it) {
+                    Single.error(Exception("${recentChange.title()} is deleted"))
+                } else {
+                    mediaClient.getMedia(recentChange.title())
+                }
+            }
+
+    /**
+     * Checks if the image exists in the reviewed images entity
+     *
+     * @param image
+     * @return
+     */
+    fun getReviewStatus(image: String?): Boolean =
+        dao?.isReviewedAlready(image) ?: false
+
+    /**
+     * Gets the first revision of the file from filename
+     *
+     * @param filename
+     * @return
+     */
+    fun getFirstRevisionOfFile(filename: String?): Observable<Revision> =
+        reviewInterface.getFirstRevisionOfFile(filename)
+            .map { it.query()?.firstPage()?.revisions()?.get(0) }
+
+    /**
+     * Checks Whether Given File is used in any Wiki page or not
+     * by calling api for given file
+     *
+     * @param filename
+     * @return
+     */
+    fun checkFileUsage(filename: String?): Observable<Boolean> =
+        reviewInterface.getGlobalUsageInfo(filename)
+            .map { it.query()?.firstPage()?.checkWhetherFileIsUsedInWikis() }
+
+    /**
+     * Checks if the change is reviewable or not.
+     * - checks the type and revisionId of the change
+     * - checks supported image extensions
+     *
+     * @param recentChange
+     * @return
+     */
+    private fun isChangeReviewable(recentChange: MwQueryPage): Boolean {
+        for (extension in imageExtensions) {
+            if (recentChange.title().endsWith(extension)) {
+                return true
+            }
+        }
+        return false
+    }
+
+    /**
+     * Adds reviewed/skipped images to the database
+     *
+     * @param imageId
+     */
+    fun addViewedImagesToDB(imageId: String?) {
+        Completable.fromAction { dao!!.insert(ReviewEntity(imageId)) }
+            .subscribeOn(Schedulers.io())
+            .observeOn(AndroidSchedulers.mainThread())
+            .subscribe(
+                {
+                    // Inserted successfully
+                    Timber.i("Image inserted successfully.")
+                }
+            ) { throwable: Throwable? -> Timber.e("Image not inserted into the reviewed images database") }
+    }
+
+    companion object {
+        private val imageExtensions = arrayOf(".jpg", ".jpeg", ".png")
+    }
+}
diff --git a/app/src/main/java/fr/free/nrw/commons/wikidata/WikiBaseClient.java b/app/src/main/java/fr/free/nrw/commons/wikidata/WikiBaseClient.java
deleted file mode 100644
index 201d97fe2..000000000
--- a/app/src/main/java/fr/free/nrw/commons/wikidata/WikiBaseClient.java
+++ /dev/null
@@ -1,76 +0,0 @@
-package fr.free.nrw.commons.wikidata;
-
-import static fr.free.nrw.commons.di.NetworkingModule.NAMED_COMMONS_CSRF;
-import static fr.free.nrw.commons.media.MediaClientKt.PAGE_ID_PREFIX;
-
-import fr.free.nrw.commons.upload.UploadResult;
-import fr.free.nrw.commons.upload.WikiBaseInterface;
-import io.reactivex.Observable;
-import javax.inject.Inject;
-import javax.inject.Named;
-import javax.inject.Singleton;
-import fr.free.nrw.commons.auth.csrf.CsrfTokenClient;
-import fr.free.nrw.commons.wikidata.mwapi.MwPostResponse;
-import timber.log.Timber;
-
-/**
- * Wikibase Client for calling WikiBase APIs
- */
-@Singleton
-public class WikiBaseClient {
-
-    private final WikiBaseInterface wikiBaseInterface;
-    private final CsrfTokenClient csrfTokenClient;
-
-    @Inject
-    public WikiBaseClient(WikiBaseInterface wikiBaseInterface,
-        @Named(NAMED_COMMONS_CSRF) CsrfTokenClient csrfTokenClient) {
-        this.wikiBaseInterface = wikiBaseInterface;
-        this.csrfTokenClient = csrfTokenClient;
-    }
-
-    public Observable<Boolean> postEditEntity(String fileEntityId, String data) {
-        return csrfToken()
-            .switchMap(editToken -> wikiBaseInterface.postEditEntity(fileEntityId, editToken, data)
-                .map(response -> (response.getSuccessVal() == 1)));
-    }
-
-    /**
-     * Makes the server call for posting new depicts
-     *
-     * @param filename name of the file
-     * @param data data of the depicts to be uploaded
-     * @return Observable<Boolean>
-     */
-    public Observable<Boolean> postEditEntityByFilename(final String filename, final String data) {
-        return csrfToken()
-            .switchMap(editToken -> wikiBaseInterface.postEditEntityByFilename(filename,
-                editToken, data)
-                .map(response -> (response.getSuccessVal() == 1)));
-    }
-
-    public Observable<Long> getFileEntityId(UploadResult uploadResult) {
-        return wikiBaseInterface.getFileEntityId(uploadResult.createCanonicalFileName())
-            .map(response -> (long) (response.query().pages().get(0).pageId()));
-    }
-
-    public Observable<MwPostResponse> addLabelstoWikidata(long fileEntityId,
-        String languageCode, String captionValue) {
-        return csrfToken()
-            .switchMap(editToken -> wikiBaseInterface
-                .addLabelstoWikidata(PAGE_ID_PREFIX + fileEntityId, editToken, languageCode,
-                    captionValue));
-
-    }
-
-    private Observable<String> csrfToken() {
-        return Observable.fromCallable(() -> {
-            try {
-                return csrfTokenClient.getTokenBlocking();
-            } catch (Throwable throwable) {
-                Timber.e(throwable);
-                return "";
-            }
-        });
-    }
-}
diff --git a/app/src/main/java/fr/free/nrw/commons/wikidata/WikiBaseClient.kt b/app/src/main/java/fr/free/nrw/commons/wikidata/WikiBaseClient.kt
new file mode 100644
index 000000000..22bb6d8b2
--- /dev/null
+++ b/app/src/main/java/fr/free/nrw/commons/wikidata/WikiBaseClient.kt
@@ -0,0 +1,69 @@
+package fr.free.nrw.commons.wikidata
+
+import fr.free.nrw.commons.auth.csrf.CsrfTokenClient
+import fr.free.nrw.commons.di.NetworkingModule
+import fr.free.nrw.commons.media.PAGE_ID_PREFIX
+import fr.free.nrw.commons.upload.UploadResult
+import fr.free.nrw.commons.upload.WikiBaseInterface
+import fr.free.nrw.commons.wikidata.mwapi.MwPostResponse
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
+import io.reactivex.Observable
+import timber.log.Timber
+import javax.inject.Inject
+import javax.inject.Named
+import javax.inject.Singleton
+
+/**
+ * Wikibase Client for calling WikiBase APIs
+ */
+@Singleton
+class WikiBaseClient @Inject constructor(
+    private val wikiBaseInterface: WikiBaseInterface,
+    @param:Named(NetworkingModule.NAMED_COMMONS_CSRF) private val csrfTokenClient: CsrfTokenClient
+) {
+    fun postEditEntity(fileEntityId: String?, data: String?): Observable<Boolean> {
+        return csrfToken().switchMap { editToken ->
+            wikiBaseInterface.postEditEntity(fileEntityId!!, editToken, data!!)
+                .map { response: MwPostResponse -> response.successVal == 1 }
+        }
+    }
+
+    /**
+     * Makes the server call for posting new depicts
+     *
+     * @param filename name of the file
+     * @param data data of the depicts to be uploaded
+     * @return Observable<Boolean>
+    </Boolean> */
+    fun postEditEntityByFilename(filename: String?, data: String?): Observable<Boolean> {
+        return csrfToken().switchMap { editToken ->
+            wikiBaseInterface.postEditEntityByFilename(filename!!, editToken, data!!)
+                .map { response: MwPostResponse -> response.successVal == 1 }
+        }
+    }
+
+    fun getFileEntityId(uploadResult: UploadResult): Observable<Long> {
+        return wikiBaseInterface.getFileEntityId(uploadResult.createCanonicalFileName())
+            .map { response: MwQueryResponse -> response.query()!!.pages()!![0].pageId().toLong() }
+    }
+
+    fun addLabelstoWikidata(fileEntityId: Long, languageCode: String?, captionValue: String?): Observable<MwPostResponse> {
+        return csrfToken().switchMap { editToken ->
+            wikiBaseInterface.addLabelstoWikidata(
+                PAGE_ID_PREFIX + fileEntityId,
+                editToken,
+                languageCode,
+                captionValue
+            )
+        }
+    }
+
+    private fun csrfToken(): Observable<String> = Observable.fromCallable {
+        try {
+            csrfTokenClient.getTokenBlocking()
+        } catch (throwable: Throwable) {
+            Timber.e(throwable)
+            ""
+        }
+    }
+}
diff --git a/app/src/main/java/fr/free/nrw/commons/wikidata/WikidataClient.java b/app/src/main/java/fr/free/nrw/commons/wikidata/WikidataClient.java
deleted file mode 100644
index 79d1e459c..000000000
--- a/app/src/main/java/fr/free/nrw/commons/wikidata/WikidataClient.java
+++ /dev/null
@@ -1,47 +0,0 @@
-package fr.free.nrw.commons.wikidata;
-
-import com.google.gson.Gson;
-import org.jetbrains.annotations.NotNull;
-
-import javax.inject.Inject;
-import javax.inject.Singleton;
-
-import fr.free.nrw.commons.wikidata.model.AddEditTagResponse;
-import io.reactivex.Observable;
-import io.reactivex.ObservableSource;
-import fr.free.nrw.commons.wikidata.model.Statement_partial;
-
-@Singleton
-public class WikidataClient {
-
-
-    private final WikidataInterface wikidataInterface;
-    private final Gson gson;
-
-    @Inject
-    public WikidataClient(WikidataInterface wikidataInterface, final Gson gson) {
-        this.wikidataInterface = wikidataInterface;
-        this.gson = gson;
-    }
-
-    /**
-     * Create wikidata claim to add P18 value
-     *
-     * @return revisionID of the edit
-     */
-    Observable<Long> setClaim(Statement_partial claim, String tags) {
-        return getCsrfToken()
-            .flatMap(
-                csrfToken -> wikidataInterface.postSetClaim(gson.toJson(claim), tags, csrfToken))
-            .map(mwPostResponse -> mwPostResponse.getPageinfo().getLastrevid());
-    }
-
-    /**
-     * Get csrf token for wikidata edit
-     */
-    @NotNull
-    private Observable<String> getCsrfToken() {
-        return wikidataInterface.getCsrfToken()
-            .map(mwQueryResponse -> mwQueryResponse.query().csrfToken());
-    }
-}
diff --git a/app/src/main/java/fr/free/nrw/commons/wikidata/WikidataClient.kt b/app/src/main/java/fr/free/nrw/commons/wikidata/WikidataClient.kt
new file mode 100644
index 000000000..d9d6dc33d
--- /dev/null
+++ b/app/src/main/java/fr/free/nrw/commons/wikidata/WikidataClient.kt
@@ -0,0 +1,32 @@
+package fr.free.nrw.commons.wikidata
+
+import com.google.gson.Gson
+import fr.free.nrw.commons.wikidata.model.Statement_partial
+import fr.free.nrw.commons.wikidata.model.WbCreateClaimResponse
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
+import io.reactivex.Observable
+import javax.inject.Inject
+import javax.inject.Singleton
+
+@Singleton
+class WikidataClient @Inject constructor(
+    private val wikidataInterface: WikidataInterface,
+    private val gson: Gson
+) {
+    /**
+     * Create wikidata claim to add P18 value
+     *
+     * @return revisionID of the edit
+     */
+    fun setClaim(claim: Statement_partial?, tags: String?): Observable<Long> {
+        return csrfToken().flatMap { csrfToken: String? ->
+            wikidataInterface.postSetClaim(gson.toJson(claim), tags!!, csrfToken!!)
+        }.map { mwPostResponse: WbCreateClaimResponse -> mwPostResponse.pageinfo.lastrevid }
+    }
+
+    /**
+     * Get csrf token for wikidata edit
+     */
+    private fun csrfToken(): Observable<String?> =
+        wikidataInterface.getCsrfToken().map { it.query()?.csrfToken() }
+}
diff --git a/app/src/test/kotlin/fr/free/nrw/commons/mwapi/UserClientTest.kt b/app/src/test/kotlin/fr/free/nrw/commons/mwapi/UserClientTest.kt
index c1075562d..b8728f485 100644
--- a/app/src/test/kotlin/fr/free/nrw/commons/mwapi/UserClientTest.kt
+++ b/app/src/test/kotlin/fr/free/nrw/commons/mwapi/UserClientTest.kt
@@ -36,7 +36,7 @@ class UserClientTest{
         Mockito.`when`(userInterface!!.getUserBlockInfo())
                 .thenReturn(Observable.just(mockResponse))
 
-        val isBanned = userClient!!.isUserBlockedFromCommons.blockingGet()
+        val isBanned = userClient!!.isUserBlockedFromCommons().blockingGet()
         assertTrue(isBanned)
     }
 
@@ -54,7 +54,7 @@ class UserClientTest{
         Mockito.`when`(userInterface!!.getUserBlockInfo())
                 .thenReturn(Observable.just(mockResponse))
 
-        val isBanned = userClient!!.isUserBlockedFromCommons.blockingGet()
+        val isBanned = userClient!!.isUserBlockedFromCommons().blockingGet()
         assertTrue(isBanned)
     }
 
@@ -69,7 +69,7 @@ class UserClientTest{
         Mockito.`when`(userInterface!!.getUserBlockInfo())
                 .thenReturn(Observable.just(mockResponse))
 
-        val isBanned = userClient!!.isUserBlockedFromCommons.blockingGet()
+        val isBanned = userClient!!.isUserBlockedFromCommons().blockingGet()
         assertFalse(isBanned)
     }
 
diff --git a/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewActivityTest.kt b/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewActivityTest.kt
index 5fffa1a2f..042559f8a 100644
--- a/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewActivityTest.kt
+++ b/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewActivityTest.kt
@@ -111,10 +111,10 @@ class ReviewActivityTest {
         val media = mock(Media::class.java)
 
         doReturn(mapOf<String, Boolean>("test" to false)).`when`(media).categoriesHiddenStatus
-        doReturn(Single.just(media)).`when`(reviewHelper)?.randomMedia
-        Assert.assertNotNull(reviewHelper?.randomMedia)
+        doReturn(Single.just(media)).`when`(reviewHelper)?.getRandomMedia()
+        Assert.assertNotNull(reviewHelper?.getRandomMedia())
         reviewHelper
-            ?.randomMedia
+            ?.getRandomMedia()
             ?.test()
             ?.assertValue(media);
         activity.swipeToNext()
diff --git a/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewDaoTest.kt b/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewDaoTest.kt
new file mode 100644
index 000000000..55623b3cb
--- /dev/null
+++ b/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewDaoTest.kt
@@ -0,0 +1,73 @@
+package fr.free.nrw.commons.review
+
+import androidx.room.Room.inMemoryDatabaseBuilder
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import fr.free.nrw.commons.TestCommonsApplication
+import fr.free.nrw.commons.db.AppDatabase
+import org.hamcrest.CoreMatchers
+import org.hamcrest.MatcherAssert
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.annotation.Config
+import org.robolectric.annotation.LooperMode
+
+@RunWith(AndroidJUnit4::class)
+@Config(sdk = [21], application = TestCommonsApplication::class)
+@LooperMode(LooperMode.Mode.PAUSED)
+class ReviewDaoTest {
+    private lateinit var  reviewDao: ReviewDao
+    private lateinit var database: AppDatabase
+
+    /**
+     * Set up the application database
+     */
+    @Before
+    fun createDb() {
+        database = inMemoryDatabaseBuilder(
+            context = ApplicationProvider.getApplicationContext(),
+            klass = AppDatabase::class.java
+        ).allowMainThreadQueries().build()
+        reviewDao = database.ReviewDao()
+    }
+
+    /**
+     * Close the database
+     */
+    @After
+    fun closeDb() {
+        database.close()
+    }
+
+    /**
+     * Test insertion
+     * Also checks isReviewedAlready():
+     * Case 1: When image has been reviewed/skipped by the user
+     */
+    @Test
+    fun insert() {
+        // Insert data
+        val imageId = "1234"
+        val reviewEntity = ReviewEntity(imageId)
+        reviewDao.insert(reviewEntity)
+
+        // Check insertion
+        // Covers the case where the image exists in the database
+        // And isReviewedAlready() returns true
+        val isInserted = reviewDao.isReviewedAlready(imageId)
+        MatcherAssert.assertThat(isInserted, CoreMatchers.equalTo(true))
+    }
+
+    @Test
+    fun isReviewedAlready() {
+        /**
+         * Test review status of the image
+         * Case 2: When image has not been reviewed/skipped
+         */
+        val imageId = "5856"
+        val isInserted = reviewDao.isReviewedAlready(imageId)
+        MatcherAssert.assertThat(isInserted, CoreMatchers.equalTo(false))
+    }
+}
\ No newline at end of file
diff --git a/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewHelperTest.kt b/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewHelperTest.kt
index 6cea81f10..74be27d5b 100644
--- a/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewHelperTest.kt
+++ b/app/src/test/kotlin/fr/free/nrw/commons/review/ReviewHelperTest.kt
@@ -1,40 +1,32 @@
 package fr.free.nrw.commons.review
 
-import com.nhaarman.mockitokotlin2.mock
 import com.nhaarman.mockitokotlin2.whenever
 import fr.free.nrw.commons.Media
 import fr.free.nrw.commons.media.MediaClient
-import io.reactivex.Completable
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryPage
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResult
 import io.reactivex.Observable
 import io.reactivex.Single
+import org.junit.Assert.assertEquals
 import org.junit.Assert.assertNull
 import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
-import org.mockito.ArgumentMatchers
-import org.mockito.InjectMocks
-import org.mockito.Mock
 import org.mockito.Mockito.*
-import org.mockito.MockitoAnnotations
-import fr.free.nrw.commons.wikidata.mwapi.MwQueryPage
-import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
-import fr.free.nrw.commons.wikidata.mwapi.MwQueryResult
-import java.util.concurrent.Callable
 
 /**
  * Test class for ReviewHelper
  */
 class ReviewHelperTest {
 
-    @Mock
-    internal var reviewInterface: ReviewInterface? = null
-    @Mock
-    internal var mediaClient: MediaClient? = null
+    private val reviewInterface = mock<ReviewInterface>()
+    private val mediaClient = mock<MediaClient>()
+    private val reviewHelper = ReviewHelper(mediaClient, reviewInterface)
 
-    @InjectMocks
-    var reviewHelper: ReviewHelper? = null
 
-    val dao = mock(ReviewDao::class.java)
+    private val mwQueryResult = mock<MwQueryResult>()
+    private val mockResponse = mock<MwQueryResponse>()
 
     /**
      * Init mocks
@@ -42,28 +34,8 @@ class ReviewHelperTest {
     @Before
     @Throws(Exception::class)
     fun setUp() {
-        MockitoAnnotations.openMocks(this)
-
-        val mwQueryPage = mock(MwQueryPage::class.java)
-        val mockRevision = mock(MwQueryPage.Revision::class.java)
-        `when`(mockRevision.user).thenReturn("TestUser")
-        `when`(mwQueryPage.revisions()).thenReturn(listOf(mockRevision))
-
-        val mwQueryResult = mock(MwQueryResult::class.java)
-        `when`(mwQueryResult.firstPage()).thenReturn(mwQueryPage)
-        `when`(mwQueryResult.pages()).thenReturn(listOf(mwQueryPage))
-        val mockResponse = mock(MwQueryResponse::class.java)
-        `when`(mockResponse.query()).thenReturn(mwQueryResult)
-        `when`(reviewInterface?.getRecentChanges())
-                .thenReturn(Observable.just(mockResponse))
-
-        `when`(reviewInterface?.getFirstRevisionOfFile(ArgumentMatchers.anyString()))
-                .thenReturn(Observable.just(mockResponse))
-
-        val media = mock(Media::class.java)
-        whenever(media.filename).thenReturn("Test file.jpg")
-        `when`(mediaClient?.getMedia(ArgumentMatchers.anyString()))
-                .thenReturn(Single.just(media))
+        whenever(mockResponse.query()).thenReturn(mwQueryResult)
+        whenever(reviewInterface.getRecentChanges()).thenReturn(Observable.just(mockResponse))
     }
 
     /**
@@ -71,14 +43,19 @@ class ReviewHelperTest {
      */
     @Test
     fun getRandomMedia() {
-        `when`(mediaClient?.checkPageExistsUsingTitle(ArgumentMatchers.anyString()))
-                .thenReturn(Single.just(false))
+        whenever(mediaClient.checkPageExistsUsingTitle(any())).thenReturn(Single.just(false))
 
-        `when`(mediaClient?.checkPageExistsUsingTitle(ArgumentMatchers.anyString()))
-                .thenReturn(Single.just(false))
+        val page1 = setupMedia("one.jpg")
+        val page2 = setupMedia("two.jpeg")
+        val page3 = setupMedia("three.png")
+        val ignored = setupMedia("ignored.txt")
+        whenever(mwQueryResult.pages()).thenReturn(listOf(page1, page2, page3, ignored))
 
-        reviewHelper?.randomMedia
-        verify(reviewInterface, times(1))!!.getRecentChanges()
+        val random = reviewHelper.getRandomMedia().test()
+
+        random.assertNoErrors()
+        assertEquals(1, random.valueCount())
+        assertTrue(setOf("one.jpg", "two.jpeg", "three.png").contains(random.values().first().filename))
     }
 
     /**
@@ -86,9 +63,12 @@ class ReviewHelperTest {
      */
     @Test(expected = RuntimeException::class)
     fun getRandomMediaWithWithAllMediaNominatedForDeletion() {
-        `when`(mediaClient?.checkPageExistsUsingTitle(ArgumentMatchers.anyString()))
-                .thenReturn(Single.just(true))
-        val media = reviewHelper?.randomMedia?.blockingGet()
+        whenever(mediaClient.checkPageExistsUsingTitle(any())).thenReturn(Single.just(true))
+
+        val page1 = setupMedia("one.jpg")
+        whenever(mwQueryResult.pages()).thenReturn(listOf(page1))
+
+        val media = reviewHelper.getRandomMedia().blockingGet()
         assertNull(media)
         verify(reviewInterface, times(1))!!.getRecentChanges()
     }
@@ -98,15 +78,14 @@ class ReviewHelperTest {
      */
     @Test
     fun getRandomMediaWithWithOneMediaNominatedForDeletion() {
-        `when`(mediaClient?.checkPageExistsUsingTitle("Commons:Deletion_requests/File:Test1.jpeg"))
-                .thenReturn(Single.just(true))
-        `when`(mediaClient?.checkPageExistsUsingTitle("Commons:Deletion_requests/File:Test2.png"))
-                .thenReturn(Single.just(false))
-        `when`(mediaClient?.checkPageExistsUsingTitle("Commons:Deletion_requests/File:Test3.jpg"))
-                .thenReturn(Single.just(true))
+        whenever(mediaClient.checkPageExistsUsingTitle("Commons:Deletion_requests/one.jpg")).thenReturn(Single.just(true))
 
-        reviewHelper?.randomMedia
-        verify(reviewInterface, times(1))!!.getRecentChanges()
+        val page1 = setupMedia("one.jpg")
+        whenever(mwQueryResult.pages()).thenReturn(listOf(page1))
+
+        val random = reviewHelper.getRandomMedia().test()
+
+        assertEquals("one.jpg is deleted", random.errors().first().message)
     }
 
     /**
@@ -114,57 +93,55 @@ class ReviewHelperTest {
      */
     @Test
     fun getFirstRevisionOfFile() {
-        val firstRevisionOfFile = reviewHelper?.getFirstRevisionOfFile("Test.jpg")?.blockingFirst()
+        val rev1 = mock<MwQueryPage.Revision>()
+        whenever(rev1.user).thenReturn("TestUser")
+        whenever(rev1.revisionId).thenReturn(1L)
+        val rev2 = mock<MwQueryPage.Revision>()
+        whenever(rev2.user).thenReturn("TestUser")
+        whenever(rev2.revisionId).thenReturn(2L)
 
-        assertTrue(firstRevisionOfFile is MwQueryPage.Revision)
+        val page = setupMedia("Test.jpg", rev1, rev2)
+        whenever(mwQueryResult.firstPage()).thenReturn(page)
+        whenever(reviewInterface.getFirstRevisionOfFile(any())).thenReturn(Observable.just(mockResponse))
+
+        val firstRevisionOfFile = reviewHelper.getFirstRevisionOfFile("Test.jpg").blockingFirst()
+
+        assertEquals(1, firstRevisionOfFile.revisionId)
     }
 
-    /**
-     * Test the review status of the image
-     *  Case 1: Image identifier exists in the database
-     */
     @Test
-    fun getReviewStatusWhenImageHasBeenReviewedAlready() {
-        val testImageId1 = "123456"
-        `when`(dao.isReviewedAlready(testImageId1)).thenReturn(true)
+    fun checkFileUsage() {
+        whenever(reviewInterface.getGlobalUsageInfo(any())).thenReturn(Observable.just(mockResponse))
+        val page = setupMedia("Test.jpg")
+        whenever(mwQueryResult.firstPage()).thenReturn(page)
+        whenever(page.checkWhetherFileIsUsedInWikis()).thenReturn(true)
 
-        val observer = io.reactivex.observers.TestObserver<Boolean>()
-        Observable.fromCallable(Callable<Boolean> {
-            dao.isReviewedAlready(testImageId1)
-        }).subscribeWith(observer)
-        observer.assertValue(true)
-        observer.dispose()
+        val result = reviewHelper.checkFileUsage("Test.jpg").test()
+
+        assertTrue(result.values().first())
     }
 
-    /**
-     * Test the review status of the image
-     *  Case 2: Image identifier does not exist in the database
-     */
     @Test
-    fun getReviewStatusWhenImageHasBeenNotReviewedAlready() {
-        val testImageId2 = "789101"
-        `when`(dao.isReviewedAlready(testImageId2)).thenReturn(false)
+    fun testReviewStatus() {
+        val reviewDao = mock<ReviewDao>()
+        whenever(reviewDao.isReviewedAlready("Test.jpg")).thenReturn(true)
 
-        val observer = io.reactivex.observers.TestObserver<Boolean>()
-        Observable.fromCallable(Callable<Boolean> {
-            dao.isReviewedAlready(testImageId2)
-        }).subscribeWith(observer)
-        observer.assertValue(false)
-        observer.dispose()
+        reviewHelper.dao = reviewDao
+        val result = reviewHelper.getReviewStatus("Test.jpg")
+
+        assertTrue(result)
     }
 
-    /**
-     * Test the successful insertion of the image identifier into the database
-     */
-    @Test
-    fun addViewedImagesToDB() {
-        val testImageId = "123456"
+    private fun setupMedia(file: String, vararg revision: MwQueryPage.Revision): MwQueryPage = mock<MwQueryPage>().apply {
+        whenever(title()).thenReturn(file)
+        if (revision.isNotEmpty()) {
+            whenever(revisions()).thenReturn(*revision.toMutableList())
+        }
 
-        val observer = io.reactivex.observers.TestObserver<Boolean>()
-        Completable.fromAction {
-            dao.insert(ReviewEntity(testImageId))
-        }.subscribeWith(observer)
-        observer.assertComplete()
-        observer.dispose()
+        val media = mock<Media>().apply {
+            whenever(filename).thenReturn(file)
+            whenever(pageId).thenReturn(file.split(".").first())
+        }
+        whenever(mediaClient.getMedia(file)).thenReturn(Single.just(media))
     }
 }
diff --git a/app/src/test/kotlin/fr/free/nrw/commons/wikidata/WikiBaseClientUnitTest.kt b/app/src/test/kotlin/fr/free/nrw/commons/wikidata/WikiBaseClientUnitTest.kt
index a42082a74..956b5d4a0 100644
--- a/app/src/test/kotlin/fr/free/nrw/commons/wikidata/WikiBaseClientUnitTest.kt
+++ b/app/src/test/kotlin/fr/free/nrw/commons/wikidata/WikiBaseClientUnitTest.kt
@@ -1,31 +1,84 @@
 package fr.free.nrw.commons.wikidata
 
+import com.nhaarman.mockitokotlin2.whenever
+import fr.free.nrw.commons.auth.csrf.CsrfTokenClient
+import fr.free.nrw.commons.upload.UploadResult
+import fr.free.nrw.commons.upload.WikiBaseInterface
+import fr.free.nrw.commons.wikidata.mwapi.MwPostResponse
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryPage
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResult
+import io.reactivex.Observable
+import junit.framework.TestCase.assertEquals
+import junit.framework.TestCase.assertSame
+import junit.framework.TestCase.assertTrue
 import org.junit.Before
 import org.junit.Test
-import org.mockito.InjectMocks
-import org.mockito.Mock
-import org.mockito.Mockito
-import org.mockito.MockitoAnnotations
-import fr.free.nrw.commons.auth.csrf.CsrfTokenClient
+import org.mockito.Mockito.mock
 
 class WikiBaseClientUnitTest {
 
-    @Mock
-    internal var csrfTokenClient: CsrfTokenClient? = null
-
-    @InjectMocks
-    var wikiBaseClient: WikiBaseClient? = null
+    private val csrfTokenClient: CsrfTokenClient = mock()
+    private val wikiBaseInterface: WikiBaseInterface = mock()
+    private val wikiBaseClient = WikiBaseClient(wikiBaseInterface, csrfTokenClient)
 
     @Before
     @Throws(Exception::class)
     fun setUp() {
-        MockitoAnnotations.openMocks(this)
-        Mockito.`when`(csrfTokenClient!!.getTokenBlocking())
-            .thenReturn("test")
+        whenever(csrfTokenClient.getTokenBlocking()).thenReturn("test")
+    }
+
+    @Test
+    fun testPostEditEntity() {
+        val response = mock<MwPostResponse>()
+        whenever(response.successVal).thenReturn(1)
+        whenever(wikiBaseInterface.postEditEntity("the-id", "test", "the-data"))
+            .thenReturn(Observable.just(response))
+
+        val result = wikiBaseClient.postEditEntity("the-id", "the-data").blockingFirst()
+
+        assertTrue(result)
     }
 
     @Test
     fun testPostEditEntityByFilename() {
-        wikiBaseClient?.postEditEntityByFilename("File:Example.jpg", "data")
+        val response = mock<MwPostResponse>()
+        whenever(response.successVal).thenReturn(1)
+        whenever(wikiBaseInterface.postEditEntityByFilename("File:Example.jpg", "test", "the-data"))
+            .thenReturn(Observable.just(response))
+
+        val result = wikiBaseClient.postEditEntityByFilename("File:Example.jpg", "the-data").blockingFirst()
+
+        assertTrue(result)
+    }
+
+    @Test
+    fun getFileEntityId() {
+        val upload = UploadResult("result", "key", 0, "Example.jpg")
+
+        val response = mock<MwQueryResponse>()
+        val query = mock<MwQueryResult>()
+        val page = mock<MwQueryPage>()
+        whenever(response.query()).thenReturn(query)
+        whenever(query.pages()).thenReturn(mutableListOf(page))
+        whenever(page.pageId()).thenReturn(123)
+        whenever(wikiBaseInterface.getFileEntityId("File:Example.jpg"))
+            .thenReturn(Observable.just(response))
+
+        val result = wikiBaseClient.getFileEntityId(upload).blockingFirst()
+
+        assertEquals(123L, result)
+    }
+
+    @Test
+    fun addLabelstoWikidata() {
+        val mwPostResponse = mock<MwPostResponse>()
+        whenever(wikiBaseInterface.addLabelstoWikidata(
+            "M123", "test", "en", "caption"
+        )).thenReturn(Observable.just(mwPostResponse))
+
+        val result = wikiBaseClient.addLabelstoWikidata(123L, "en", "caption").blockingFirst()
+
+        assertSame(mwPostResponse, result)
     }
 }
\ No newline at end of file
diff --git a/app/src/test/kotlin/fr/free/nrw/commons/wikidata/WikidataEditServiceTest.kt b/app/src/test/kotlin/fr/free/nrw/commons/wikidata/WikidataEditServiceTest.kt
index 041a0fa97..b4d4a4af5 100644
--- a/app/src/test/kotlin/fr/free/nrw/commons/wikidata/WikidataEditServiceTest.kt
+++ b/app/src/test/kotlin/fr/free/nrw/commons/wikidata/WikidataEditServiceTest.kt
@@ -2,6 +2,7 @@ package fr.free.nrw.commons.wikidata
 
 import android.content.Context
 import com.google.gson.Gson
+import com.nhaarman.mockitokotlin2.anyOrNull
 import com.nhaarman.mockitokotlin2.mock
 import com.nhaarman.mockitokotlin2.whenever
 import fr.free.nrw.commons.kvstore.JsonKvStore
@@ -61,7 +62,7 @@ class WikidataEditServiceTest {
     fun createImageClaim() {
         whenever(directKvStore.getBoolean("Picture_Has_Correct_Location", true))
             .thenReturn(true)
-        whenever(wikibaseClient.getFileEntityId(any())).thenReturn(Observable.just(1L))
+        whenever(wikibaseClient.getFileEntityId(anyOrNull())).thenReturn(Observable.just(1L))
         whenever(wikidataClient.setClaim(any(), anyString()))
             .thenReturn(Observable.just(1L))
         val wikidataPlace: WikidataPlace = mock()