IvanShafran

public class CounterPreferences {
    // ...
    private final SharedPreferences sharedPreferences;
    public CounterPreferences(@NonNull final Context context) {
        sharedPreferences = context.getSharedPreferences(FILENAME, Context.MODE_PRIVATE);
    }

    public int getCounter() {
        return sharedPreferences.getInt(KEY, 0);
    }

IvanShafran

allprojects {
    repositories {
        ...
        maven { url 'https://jitpack.io' }
    }
}

IvanShafran

dependencies {
    testImplementation 'com.github.IvanShafran:shared-preferences-mock:1.0'
}

IvanShafran

class BuyPreferencesImpl(context: Context) : BuyPreferences {
    companion object {
        private val PREFERENCES_FILENAME = "BUY_PREFERENCES"
        private val BUY_COUNT_KEY = "BUY_COUNT_KEY"
    }

    private val sharedPreferences = context.getSharedPreferences(
        PREFERENCES_FILENAME, 
        Context.MODE_PRIVATE
    )

IvanShafran

interface BuyPreferences {
    fun incrementBuyCount()
    fun getBuyCount(): Int
}

class BuyPreferencesImpl(context: Context) : BuyPreferences {
    // ...
    private val sharedPreferences: SharedPreferences = context.getSharedPreferences(...)

    override fun incrementBuyCount() {

IvanShafran

interface Time {
    fun getCurrentTimeMillis(): Long
}

class TimeImpl : Time {
    override fun getCurrentTimeMillis() = System.currentTimeMillis()
}

IvanShafran

class ShowRateUsLogic(
    private val rateUsPreferences: RateUsPreferences,
    private val buyPreferences: BuyPreferences,
    private val time: Time
) {
    fun shouldShowRateUs(): Boolean {
        val timeFromLastShown = time.getCurrentTimeMillis() - rateUsPreferences.getLastShownTimeMillis()
        return when {
            // User doesn't want to see "rate us" again
            rateUsPreferences.isNeverShownAgainClicked() -> false

IvanShafran

public class BuyPreferencesMock implements BuyPreferences {
    private int count;

    @Override public void incrementBuyCount() {
        ++count;
    }

    @Override public int getBuyCount() {
        return count;
    }

IvanShafran

public class ShowRateUsLogicTest {
    private RateUsPreferencesMock rateUsPreferences;
    private BuyPreferencesMock buyPreferences;
    private TimeMock time;
    private ShowRateUsLogic showRateUsLogic;

    @Test public void test1() {
        rateUsPreferences = new RateUsPreferencesMock();
        buyPreferences = new BuyPreferencesMock();
        time = new TimeMock();

IvanShafran

class ShowRateUsLogicTest {
    // property declaration and setup are skipped
    private fun prepareConditions(
        buyClickedTimes: Int = 0, 
        isNeverShownAgainClicked: Boolean = false,
        isRateNowClicked: Boolean = false, 
        lastShownTimeMillis: Long = 0, 
        currentTimeMillis: Long = 0
    ) {
        repeat(buyClickedTimes) { buyPreferences.incrementBuyCount() }