android - Need help to write a unit test using Mockito and JUnit4

Question

Need help to write a unit test for the below code using Mockito and JUnit4,

public class MyFragmentPresenterImpl { 
      public Boolean isValid(String value) {
        return !(TextUtils.isEmpty(value));
      }
}

I tried below method: MyFragmentPresenter mMyFragmentPresenter

@Before
public void setup(){
    mMyFragmentPresenter=new MyFragmentPresenterImpl();
}

@Test
public void testEmptyValue() throws Exception {
    String value=null;
    assertFalse(mMyFragmentPresenter.isValid(value));
}

but it returns following exception,

java.lang.RuntimeException: Method isEmpty in android.text.TextUtils not mocked. See http://g.co/androidstudio/not-mocked for details. at android.text.TextUtils.isEmpty(TextUtils.java) at ....

Answer 1

Because of JUnit TestCase class cannot use Android related APIs, we have to Mock it.
Use PowerMockito to Mock the static class.

Add two lines above your test case class,

@RunWith(PowerMockRunner.class)
@PrepareForTest(TextUtils.class)
public class YourTest
{

}

And the setup code

@Before
public void setup() {
    PowerMockito.mockStatic(TextUtils.class);
    PowerMockito.when(TextUtils.isEmpty(any(CharSequence.class))).thenAnswer(new Answer<Boolean>() {
        @Override
        public Boolean answer(InvocationOnMock invocation) throws Throwable {
            CharSequence a = (CharSequence) invocation.getArguments()[0];
            return !(a != null && a.length() > 0);
        }
    });
}

That implement TextUtils.isEmpty() with our own logic.

Also, add dependencies in app.gradle files.

testCompile "org.powermock:powermock-module-junit4:1.6.2"
testCompile "org.powermock:powermock-module-junit4-rule:1.6.2"
testCompile "org.powermock:powermock-api-mockito:1.6.2"
testCompile "org.powermock:powermock-classloading-xstream:1.6.2"

Thanks Behelit's and Exception's answer.