A useful base class for unit testing database code

InMemoryDatabaseTest.kt

package fr.free.nrw.commons

import android.database.Cursor
import androidx.room.Room
import androidx.test.core.app.ApplicationProvider
import fr.free.nrw.commons.data.DBOpenHelper
import fr.free.nrw.commons.db.AppDatabase
import junit.framework.TestCase.assertTrue
import org.junit.After
import org.junit.Assert.assertEquals
import org.junit.runner.RunWith
import org.robolectric.RobolectricTestRunner
import org.robolectric.annotation.Config

@RunWith(RobolectricTestRunner::class)
@Config(sdk = [21], application = TestCommonsApplication::class)
abstract class InMemoryDatabaseTest {
    val roomDatabase: AppDatabase by lazy {
        Room.inMemoryDatabaseBuilder(
            context = ApplicationProvider.getApplicationContext(),
            klass = AppDatabase::class.java
        ).build()
    }

    val openHelper: DBOpenHelper by lazy {
        DBOpenHelper(roomDatabase.openHelper)
    }

    @After
    fun cleanup() {
        roomDatabase.close()
    }

    fun clearAllTables() = roomDatabase.clearAllTables()

    // Just test that there is a table with the correct name
    fun assertTablesExist(vararg tableNames: String) {
        tableNames.forEach(::assertTableExists)
    }

    // Test that the given table exists, and if you give field names, verify they exist in
    // that table.
    fun assertTableExists(tableName: String, expectedFields: Array<String> = emptyArray()) {
        var cursor: Cursor? = null
        try {
            cursor = openHelper.writableDatabase.query(
                "select * from $tableName where 0=1"
            )

            if (expectedFields.isNotEmpty()) {
                assertEquals(
                    "Wrong column count for \"$tableName\"",
                    expectedFields.size, cursor.columnCount
                )
                expectedFields.forEach {
                    // Unknown fields have a negative index
                    assertTrue(
                        "Field \"$it\" not found in \"$tableName\"",
                        cursor.getColumnIndex(it) >= 0
                    )
                }
            }
        } finally {
            cursor?.close()
        }
    }

    fun assertRowCount(tableName: String, expectedCount: Int) {
        var cursor: Cursor? = null
        try {
            cursor = openHelper.writableDatabase.query(
                "select count(*) from $tableName"
            )
            assertTrue(cursor.moveToFirst())
            val actualCount = cursor.getInt(0)
            assertEquals("Wrong row count for \"$tableName\"", expectedCount, actualCount)
        } finally {
            cursor?.close()
        }
    }
}

class CategoryTableTest : InMemoryDatabaseTest() {
    @Test
    fun createTable() {
        CategoryTable.onCreate(openHelper.writableDatabase)
        assertTableExists(CategoryTable.TABLE_NAME, CategoryTable.ALL_FIELDS)
    }
}