Add test for error alert dialog to UploadCategoriesFragment unit tests

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

@@ -153,6 +153,13 @@ class UploadCategoriesFragmentUnitTests {
         fragment.showError(R.string.no_categories_found)
     }
 
+    @Test
+    @Throws(Exception::class)
+    fun testShowErrorDialog() {
+        Shadows.shadowOf(Looper.getMainLooper()).idle()
+        fragment.showErrorDialog("")
+    }
+
     @Test
     @Throws(Exception::class)
     fun testSetCategoriesCaseNull() {