Android unit testing and interfaces

I have been having quite a bit of trouble implementing unit testing on the Android. As a simple test, I've been trying to match a string retrieved from string resources:

String myString = myActivity.getResources().getString(R.string.testString));

However, when unit testing this invariably results in a null pointer exception. This includes robolectric as well as the Junit implementation delivered with the Android sdk.

One possible solution is to approach the retrieval of resources in a manner similar to a data access object. That is, create an interface through which string resources would be accessed. This would allow me to mock access the string resource. Similarly, I could separate the non-android dependent behavior of, say, an Activity, into a separate pojo class. This would allow me to run开发者_JAVA百科 unit tests using standard Java testing tools. In fact, I could potentially delegate any Android infrastructure related activity to an interface.

This seems like a lot of jumping through hoops to get to unit testing. Is it worth it? Is there a more viable approach?

It turned out, the problem was that the activity has to be gotten in the actual test method. So, for example, my method now looks like this:

public void testGetActivityResourceString() {

    Activity myActivity = this.getActivity();
    String myString = myActivity.getResources().getString(R.string.hello);
    Assert.assertNotNull(myString);
}

Whereas before I was creating activity in setup. This giveaway was in the docs:

"For each test method invocation, the Activity will not actually be created until the first time this method is called."

This was a real hassle to figure out. The example for HelloWorldTest doesn't work for the same reason.

Here's the full entry:

Public T getActivity () Since: API Level 3 Get the Activity under test, starting it if necessary.

For each test method invocation, the Activity will not actually be created until the first time this method is called.

If you wish to provide custom setup values to your Activity, you may call setActivityIntent(Intent) and/or setActivityInitialTouchMode(boolean) before your first call to getActivity(). Calling them after your Activity has started will have no effect.

NOTE: Activities under test may not be started from within the UI thread. If your test method is annotated with UiThreadTest, then your Activity will be started automatically just before your test method is run. You still call this method in order to get the Activity under test.

This works correctly:

public void testGetResourceString() {
    assertNotNull(mActivity.getResources()
          .getString(com.example.pkg.R.string.testString));
}

Because you haven't provided any of your code but only the getReousrces() line, I will guess what you are doing wrong:

1. you are not using the correct base class for your test, use ActivityInstrumentationTestCase2 because you need the system infrastructure
2. you are using the resources of your test project instead of your project under test, that's why in my example the id is com.example.pkg.R.string.testString.