Adds a Test for Method A categories search (commons-app#3366)

* CategoriesModelTest: add methodA test for categories search

* CategoriesModelTest: use lateinit wherever possible

* CategoriesModelTest: make method name meaningful

Author: kbhardwaj123

app/src/test/kotlin/fr/free/nrw/commons/category/CategoriesModelTest.kt

@@ -8,6 +8,9 @@ import org.mockito.*
 import org.wikipedia.dataclient.mwapi.MwQueryPage
 import org.wikipedia.dataclient.mwapi.MwQueryResponse
 import org.wikipedia.dataclient.mwapi.MwQueryResult
+import android.content.Context
+import com.google.gson.Gson
+import fr.free.nrw.commons.kvstore.JsonKvStore
 
 //class for testing CategoriesModel class
 class CategoriesModelTest {
@@ -17,12 +20,26 @@ class CategoriesModelTest {
     @Mock
     internal var categoryItem: CategoryItem? = null
 
+    @Spy
+    internal lateinit var gson: Gson
+
+    @Spy
+    internal lateinit var categoryItemForSubstringSearch: CategoryItem
+
+    @Mock
+    internal var categoryDao: CategoryDao? = null
+
+    @Mock
+    internal var context: Context? = null
+
     @InjectMocks
     var categoryClient: CategoryClient? = null
 
     @Before
     @Throws(Exception::class)
     fun setUp() {
+        gson = Gson()
+        categoryItemForSubstringSearch = CategoryItem("",false)
         MockitoAnnotations.initMocks(this)
     }
 
@@ -47,4 +64,42 @@ class CategoriesModelTest {
         val actualCategoryNameCaps = categoriesModel!!.searchAll("Tes",null).blockingFirst()
         assertEquals("Test", actualCategoryNameCaps.getName())
     }
+
+    /**
+    * For testing the substring search algorithm for Categories search
+    * To be more precise it tests the In Between substring( ex: searching `atte` 
+    * will give search suggestions: `Latte`, `Iced latte` e.t.c) which has been described 
+    * on github repo wiki: 
+    * https://github.com/commons-app/apps-android-commons/wiki/Category-suggestions-(readme)#user-content-3-category-search-when-typing-in-the-search-field-has-been-made-more-flexible
+    */
+    @Test
+    fun searchAllFoundCaseTestForSubstringSearch() {
+        val mockDaoList = mutableListOf<String>("")
+        val mwQueryPage = Mockito.mock(MwQueryPage::class.java)
+        Mockito.`when`(mwQueryPage.title()).thenReturn("Category:Test")
+        val mwQueryResult = Mockito.mock(MwQueryResult::class.java)
+        Mockito.`when`(mwQueryResult.pages()).thenReturn(listOf(mwQueryPage))
+        val mockResponse = Mockito.mock(MwQueryResponse::class.java)
+        Mockito.`when`(mockResponse.query()).thenReturn(mwQueryResult)
+        Mockito.`when`(context!!.getSharedPreferences("",0))
+                .thenReturn(null)
+        val directKvStore = Mockito.spy(JsonKvStore(context,"",gson))
+        val categoriesModelForSubstringSearch = Mockito.spy(CategoriesModel(categoryClient,categoryDao,directKvStore))
+        Mockito.doReturn(Observable.just(categoryItemForSubstringSearch)).`when`(categoriesModelForSubstringSearch).gpsCategories()
+        Mockito.`when`(context!!.getSharedPreferences("",0))
+                .thenReturn(null)
+        Mockito.`when`(categoryInterface!!.searchCategories(ArgumentMatchers.anyString(), ArgumentMatchers.anyInt(), ArgumentMatchers.anyInt()))
+                .thenReturn(Observable.just(mockResponse))
+        Mockito.doReturn(mockDaoList).`when`(categoryDao)?.recentCategories(25)
+        Mockito.doReturn("Random Value").`when`(directKvStore).getString("Category","")
+        Mockito.`when`(categoryInterface!!.searchCategories(ArgumentMatchers.anyString(), ArgumentMatchers.anyInt(), ArgumentMatchers.anyInt()))
+                .thenReturn(Observable.just(mockResponse))
+
+        // Checking if both return "Test"
+        val actualCategoryName = categoriesModelForSubstringSearch!!.searchAll(null, listOf<String>("tes")).blockingLast()
+        assertEquals("Test",actualCategoryName.getName())
+
+        val actualCategoryNameCaps = categoriesModelForSubstringSearch!!.searchAll(null, listOf<String>("Tes")).blockingLast()
+        assertEquals("Test",actualCategoryNameCaps.getName())
+    }
 }