How to write test cases for Callbacks in android?

Question

I want to write a test case for an override method that just calls another task, but doesn't return anything.

Answer 1

Here is one simple example:

build.gradle:

    testImplementation 'junit:junit:4.12'
    testImplementation 'org.powermock:powermock-module-junit4:1.6.6'
    testImplementation 'org.powermock:powermock-module-junit4-rule:1.6.6'
    testImplementation 'org.powermock:powermock-api-mockito:1.6.6'
    testImplementation 'org.powermock:powermock-classloading-xstream:1.6.6'
    testImplementation 'org.robolectric:robolectric:3.3.2'
    testImplementation "org.robolectric:robolectric-annotations:3.3.2"
    testImplementation "org.robolectric:shadows-support-v4:3.3.2"

AppUtils.java. Here we have two methods to test.

package com.example.myapplication.utils;

import android.content.Context;
import android.util.Log;

public class AppUtils {
    public interface TResultRunnable <T>{
        public void onSuccess(T result);
        public void onFail(Exception e);
    }
    public static void parseIntWithCallback(String value, TResultRunnable<Integer> tResultRunnable ){
        int intVal = 0;
        try {
            intVal = Integer.parseInt(value);
            tResultRunnable.onSuccess(intVal);
        } catch (Exception e) {
            tResultRunnable.onFail(e);
        }
    }
    public static void parseIntWithCallback2(Context context, String value, TResultRunnable<Integer> tResultRunnable ){
        Log.i("test", "method begin. package="+context.getPackageName());

        int intVal = 0;
        try {
            intVal = Integer.parseInt(value);
            tResultRunnable.onSuccess(intVal);
            Log.i("test", "method success");

        } catch (Exception e) {
            Log.e("test", "method exception "+e);
            tResultRunnable.onFail(e);
        }
    }


}

ExampleUnitTest.java in src/test/java/com/example/myapplication folder.

package com.example.myapplication;

import android.content.Context;
import android.util.Log;

import com.example.myapplication.utils.AppUtils;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

import static org.mockito.Mockito.*;

@RunWith(PowerMockRunner.class)
@PrepareForTest({AppUtils.class, Log.class})
public class ExampleUnitTest {
    @Before
    public void setUp() {
        PowerMockito.mockStatic(Log.class);
    }
    @Test
    public void test_parseInt() {
        {
            AppUtils.TResultRunnable<Integer> mockListener = mock(AppUtils.TResultRunnable.class);
            AppUtils.parseIntWithCallback("1000", mockListener);
            verify(mockListener, never()).onFail(any(Exception.class));
            verify(mockListener, times(1)).onSuccess(1000);
        }
        {
            AppUtils.TResultRunnable<Integer> mockListener = mock(AppUtils.TResultRunnable.class);
            AppUtils.parseIntWithCallback("xxx", mockListener);
            verify(mockListener, times(1)).onFail(any(Exception.class));
            verify(mockListener, never()).onSuccess(anyInt());
        }
    }
    @Test
    public void test_parseIntWithCallback2() {
        Context context = mock(Context.class);

        {
            AppUtils.TResultRunnable<Integer> mockListener = mock(AppUtils.TResultRunnable.class);
            AppUtils.parseIntWithCallback2(context, "1000", mockListener);
            verify(mockListener, never()).onFail(any(Exception.class));
            verify(mockListener, times(1)).onSuccess(1000);
        }
        {
            AppUtils.TResultRunnable<Integer> mockListener = mock(AppUtils.TResultRunnable.class);
            AppUtils.parseIntWithCallback2(context, "xxx", mockListener);
            verify(mockListener, times(1)).onFail(any(Exception.class));
            verify(mockListener, never()).onSuccess(anyInt());
        }
    }

}