Refactoring to extract GpsCategoryModel and ensure single-responsibility-principle is maintained in CategoryApi.

app/src/test/kotlin/fr/free/nrw/commons/upload/GpsCategoryModelTest.kt

@@ -0,0 +1,77 @@
+package fr.free.nrw.commons.upload
+
+import org.junit.Assert.*
+import org.junit.Before
+import org.junit.Test
+
+class GpsCategoryModelTest {
+
+    private lateinit var testObject : GpsCategoryModel
+
+    @Before
+    fun setUp() {
+        testObject = GpsCategoryModel()
+    }
+
+    @Test
+    fun initiallyTheModelIsEmpty() {
+        assertFalse(testObject.gpsCatExists)
+        assertTrue(testObject.categoryList.isEmpty())
+    }
+
+    @Test
+    fun addingCategoriesToTheModel() {
+        testObject.add("one")
+        assertTrue(testObject.gpsCatExists)
+        assertFalse(testObject.categoryList.isEmpty())
+        assertEquals(listOf("one"), testObject.categoryList)
+    }
+
+    @Test
+    fun duplicatesAreIgnored() {
+        testObject.add("one")
+        testObject.add("one")
+        assertEquals(listOf("one"), testObject.categoryList)
+    }
+
+    @Test
+    fun modelProtectsAgainstExternalModification() {
+        testObject.add("one")
+
+        val list = testObject.categoryList
+        list.add("two")
+
+        assertEquals(listOf("one"), testObject.categoryList)
+    }
+
+    @Test
+    fun clearingTheModel() {
+        testObject.add("one")
+
+        testObject.clear()
+        assertFalse(testObject.gpsCatExists)
+        assertTrue(testObject.categoryList.isEmpty())
+
+        testObject.add("two")
+        assertEquals(listOf("two"), testObject.categoryList)
+    }
+
+    @Test
+    fun settingTheListHandlesNull() {
+        testObject.add("one")
+
+        testObject.categoryList = null
+
+        assertFalse(testObject.gpsCatExists)
+        assertTrue(testObject.categoryList.isEmpty())
+    }
+
+    @Test
+    fun setttingTheListOverwritesExistingValues() {
+        testObject.add("one")
+
+        testObject.categoryList = listOf("two")
+
+        assertEquals(listOf("two"), testObject.categoryList)
+    }
+}