如何在 Robolectric 单元测试中断言 void 方法

Question

How to verify a void method call in Robolectric test case where as no data coming out the called method.

What to assert in this case? Below given an example of the requirement.

public class SampleClass(){

    final String TAG = SampleClass.class.getSimpleName();

    public void log(){
        Log.d(TAG, "Entry Loggd");
    }

}

@Test
public void logEntry_test(){

    SampleClass sc = new SampleClass();
    sc.log();

    // What to assert here to verify this log method

}

Answer 1

First off, good on you for writing tests!!! There are a few ways to go about testing that an internal logger is called. It's equally as important to understand what you're looking to test. Testing that a class is logging a specific message is most likely a fragile test , so be fore-warned that you probably don't need it.

Method #1: Using Robolectric

Robolectic documentation doesn't lend itself to answering basic questions, but its codebase is very well documented with its tests. A basic understanding of its principles and how shadows work can get you a long way. ShadowLog tests lay the ground work to this solution.

@RunWith(RobolectricTestRunner.class)
public class SampleClassTest {
    @Test
    public void log_writesExpectedMessage() {
        new SampleClass().log();

        ShadowLog.LogItem lastLog = ShadowLog.getLogs().get(0);
        assertThat(lastLog.msg).isEqualTo("some message");
        // or
        assertThat(lastLog.msg).isNotNull();
    }
}

Tests using Robolectric v3.1.2 Add the following to your build.gradle file:

testCompile 'org.robolectric:robolectric:3.1.2'

Method #2: Making use of Abstractions

If your sample class derives from an Android class (Activity, Fragment, Application, etc), then using android.util.Log makes sense, but bear in mind that your test will need to be a Robolectric or AndroidInstrumented test. If your SampleClass is just some POJO, then using a simple logging framework may make your testing efforts easier. For example, using Jake Wharton's Timber , your class and test can be written as follows:

import timber.log.Timber;

public class SampleClass {
    void log() {
        Timber.d("some message");
    }
}

// SampleClassTest.java
public class SampleClassTest {
    // setting up a Tree instance that we define below
    TestTree testTree = new TestTree();

    @Test
    public void log_writesExpectedMessage() {
        // setting up Timber to us the test classes log writer
        Timber.plant(testTree);
        // invoke the logging function
        new SampleClass().log();
        // assert
        assertThat(testTree.lastMessage).isEqualTo("some message");
    }

    private class TestTree extends Timber.Tree {
        private String lastMessage;

        @Override
        protected void log(int priority, String tag, String message, Throwable t) {
            lastMessage = message;
        }
    }
}

Good luck, happy testing!

Answer 2

In my understanding you want to mock static methods. I guess, using static mocks are not the most elegant way to testing. Better to use an abstraction as recommended by abest . Although, it can be done with PowerMock .