gcloud-java provides tools to make testing your application easier.

You can test against a temporary local datastore by following these steps:

1. Start the local datastore emulator using `LocalGcdHelper`. This can be done in two ways:

- Run `LocalGcdHelper.java`'s `main` method with arguments `START` and (optionally) `--port=<port number>`. This will create a temporary folder on your computer and bind `localhost:<port number>` for communication with the local datastore. The port number is an optional argument. If no port number is specified, port 8080 will be used.

- Call `LocalGcdHelper.start(<project ID>, <port number>)` before running your tests. Save the `LocalGcdHelper` object returned so that you can stop the emulator later.

2. In your program, create and use a datastore whose host is set host to `localhost:<port number>`. For example,

```java

DatastoreOptions options = DatastoreOptions.builder()

.projectId(PROJECT_ID)

.host("localhost:8080")

.build();

Datastore localDatastore = DatastoreFactory.instance().get(options);

```

3. Run your tests.

4. Stop the local datastore emulator.

- If you ran `LocalGcdHelper.java`'s `main` function to start the emulator, run `LocalGcdHelper.java`'s `main` method with arguments `STOP` and (optionally) `--port=<port number>`. If the port is not supplied, the program will attempt to close the last port started.

- If you ran `LocalGcdHelper.start()` to start the emulator, call the `stop()` method on the `LocalGcdHelper` object returned by `LocalGcdHelper.start()`.

You can test against a remote datastore emulator as well. To do this, set the `DatastoreOptions` project endpoint to the hostname of the remote machine, like the example below.

```java

DatastoreOptions options = DatastoreOptions.builder()

.projectId(PROJECT_ID)

.host("http://<hostname of machine>")

.build();

Datastore localDatastore = DatastoreFactory.instance().get(options);

```

Note that the remote datastore must be running before your tests are run. Also note that the `host` argument must start with "http://" or "https://".

There currently isn't an emulator for Google Cloud Storage, so an alternative is to create a test project. `RemoteGcsHelper` contains convenience methods to make setting up and cleaning up the test project easier. To use this class, follow the steps below:

1. Create a test Google App Engine project.

2. Create and download a JSON key by going to the Google Developer's Console and clicking API's & Auth > Credentials > Add Credentials > Service Credentials. Choose "JSON", download the file, and note its location.

3. Set environment variables `GCLOUD_TESTS_PROJECT_ID` and `GCLOUD_TESTS_KEY_PATH` according to your test project's ID and the location of the newly-downloaded JSON key file.

4. Create and and use a `RemoteGcsHelper` object.

Here is an example that uses the RemoteGcsHelper to create a bucket and clear the bucket at the end of the test.

RemoteGcsHelper gcsHelper = RemoteGcsHelper.create();

Storage storage = StorageFactory.instance().get(gcsHelper.options());

String bucket = RemoteGcsHelper.generateBucketName();

storage.create(BucketInfo.of(bucket));

RemoteGcsHelper.deleteBucketRecursively(storage, bucket, 5, TimeUnit.SECONDS);