Migrating Junit4 tests to androidx: What causes 'delegate runner could not be loaded'?

Question

I am migrating my app to androidx, I can\'t seem to get my unit tests working. I took example from Google\'s AndroidJunitRunnerSample, which has been updated to use the new

Answer 1

In my case, I skipped annotate test case with @Test. It is not your case. This answer is for others like me.

Answer 2

While testing for activity make sure ActivityTestRule variable is public :

@Rule
public ActivityTestRule<YourActivity> activityTestRule = new ActivityTestRule<>(YourActivity.class); 

Answer 3

The error message displayed when I delete the @Test method.

You can try to put a @Test method and run

@Test
public void signInTest() {


}

Answer 4

In my case, I fixed it by explicitly declaring all @Test, @Before, and @After methods aspublic, and declaring @BeforeClass and @AfterClass as public static

If you leave any of those methods as implicitly/explicitly protected, or explicitly private; you'll encounter the following exception

java.lang.RuntimeException: Delegate runner 'androidx.test.internal.runner.junit4.AndroidJUnit4ClassRunner' for AndroidJUnit4 could not be loaded.

So, the correct thing is to use

@Before
public void setUp() {

}

@BeforeClass
public static void init() {

}

Instead of:

@Before
void setUp() {

}

@Before
protected void setUp() {

}

@Before
private void setUp() {

}

@BeforeClass
public void init() {

}

Answer 5

The testing framework actually give too little information. I encountered the same issue and dug into the stack trace, and found these validation:

So you must declare your @BeforeClass method static.

Answer 6

There are 2 ways that you can try to resolve this problem:

Solution 1:

Build --> Clean Project. Then Build --> Rebuild Project

Solution 2:

There are 2 packages that has of AndroidJUnit4

1. androidx.test.runner (deprecated)
2. androidx.test.ext.junit.runners

Make sure your build.gradle (app) has this line

android {
    defaultConfig {
    ....
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    ....
    }
}

and make sure you use (1) (which is deprecated) instead of (2) (new but not stable yet) in @RunWith(AndroidJUnit4.class) before your test class.