### Question:
FirebaseAuthProvider implements AuthProvider { @Override public boolean isUserSignedIn() { return mFirebaseAuth != null && mFirebaseAuth.getCurrentUser() != null; } FirebaseAuthProvider(
            @Nullable FirebaseAuth firebaseAuth,
            GoogleAuthProvider googleProvider); @Override void onStart(); @Override void onStop(); @Override boolean isUserSignedIn(); @Override @Nullable User getCurrentUser(); @Nullable Task<GetTokenResult> getUserToken(boolean forceRefresh); @Nullable @Override Intent buildSignInIntent(); @Override Observable<FirebaseSignInUser> userFromSignInResult(int requestCode, int resultCode, Intent data); Observable<FirebaseSignInUser> signInLegacyUser();  }### Answer:
@Test public void isUserSignedIn() { assertFalse(mFirebaseAuthProvider.isUserSignedIn()); FirebaseUser user = Mockito.mock(FirebaseUser.class); when(mFirebaseAuth.getCurrentUser()).thenReturn(user); assertTrue(mFirebaseAuthProvider.isUserSignedIn()); }