Testing Your Content Provider

If you are implementing a content provider to store and retrieve data or to make data accessible to other apps, you should test your provider to ensure that it doesn't behave in an unexpected way. This lesson describes how to test public content providers, and is also applicable to providers that you keep private to your own app.

Create Integration Tests for Content Providers

In Android, apps view content providers as data APIs that provide tables of data, with their internals hidden from view. A content provider may have many public constants, but it usually has few if any public methods and no public variables. For this reason, you should write your tests based only on the provider's public members. A content provider that is designed like this is offering a contract between itself and its users.

Content providers let you access actual user data, so it's important to ensure that you test the content provider in an isolated testing environment. This approach allows you to only run against data dependencies set explicitly in the test case. It also means that your tests do not modify actual user data. For example, you should avoid writing a test that fails because there was data left over from a previous test. Similarly, your test should avoid adding or deleting actual contact information in a provider.

To test your content provider in isolation, use the ProviderTestCase2 class. This class allows you to use Android mock object classes such as IsolatedContext and MockContentResolver to access file and database information without affecting the actual user data.

Your integration test should be written as a JUnit 4 test class. To learn more about creating JUnit 4 test classes and using JUnit 4 assertions, see Create a Local Unit Test Class.

To create an integration test for your content provider, you must perform these steps:

• Create your test class as a subclass of ProviderTestCase2.
• Add the @RunWith(AndroidJUnit4.class) annotation at the beginning of your test class definition.
• Specify the AndroidJUnitRunner class that the Android Testing Support Library provides as your default test runner. This step is described in more detail in Getting Started with Testing.
• Set the Context object from the InstrumentationRegistry class. See the snippet below for an example.

  @Override
  protected void setUp() throws Exception {
      setContext(InstrumentationRegistry.getTargetContext());
      super.setUp();
  }

How ProviderTestCase2 works

You test a provider with a subclass of ProviderTestCase2. This base class extends AndroidTestCase, so it provides the JUnit testing framework as well as Android-specific methods for testing application permissions. The most important feature of this class is its initialization, which creates the isolated test environment.

The initialization is done in the constructor for ProviderTestCase2, which subclasses call in their own constructors. The ProviderTestCase2 constructor creates an IsolatedContext object that allows file and database operations but stubs out other interactions with the Android system. The file and database operations themselves take place in a directory that is local to the device or emulator and has a special prefix.

The constructor then creates a MockContentResolver to use as the resolver for the test.

Lastly, the constructor creates an instance of the provider under test. This is a normal ContentProvider object, but it takes all of its environment information from the IsolatedContext, so it is restricted to working in the isolated test environment. All of the tests done in the test case class run against this isolated object.

You run integration tests for content providers the same way as instrumented unit tests. To run the integration test for your content provider, follow the steps described in Run Instrumented Unit Tests.

What to Test

Here are some specific guidelines for testing content providers.

• Test with resolver methods: Even though you can instantiate a provider object in ProviderTestCase2, you should always test with a resolver object using the appropriate URI. Doing so ensures that you are testing the provider by performing the same interaction that a regular application would use.
• Test a public provider as a contract: If you intend your provider to be public and available to other applications, you should test it as a contract. Some examples of how to do so are as follows:
  • Test with constants that your provider publicly exposes. For example, look for constants that refer to column names in one of the provider's data tables. These should always be constants publicly defined by the provider.
  • Test all the URIs that your provider offers. Your provider may offer several URIs, each one referring to a different aspect of the data.
  • Test invalid URIs: Your unit tests should deliberately call the provider with an invalid URI, and look for errors. A good provider design is to throw an IllegalArgumentException for invalid URIs.
• Test the standard provider interactions: Most providers offer six access methods: query(), insert(), delete(), update(), getType(), and onCreate(). Your tests should verify that all of these methods work. These methods are described in more detail in the topic Content Providers.
• Test business logic: If the content provider implements business logic, you should test it. Business logic includes handling of invalid values, financial or arithmetic calculations, elimination or combining of duplicates.