Testing is a crucial part of your application, and as information retrieval itself is already a complex topic, there should not be any additional complexity in setting up a testing infrastructure, which uses Elasticsearch. This is the main reason why we decided to release an additional file to the release, which allows you to use the same testing infrastructure we do in the Elasticsearch core. The testing framework allows you to setup clusters with multiple nodes in order to check if your code covers everything needed to run in a cluster. The framework prevents you from writing complex code yourself to start, stop or manage several test nodes in a cluster. In addition there is another very important feature called randomized testing, which you are getting for free as it is part of the Elasticsearch infrastructure.
The key concept of randomized testing is not to use the same input values for every testcase, but still be able to reproduce it in case of a failure. This allows to test with vastly different input variables in order to make sure, that your implementation is actually independent from your provided test data.
All of the tests are run using a custom junit runner, the `RandomizedRunner` provided by the randomized-testing project. If you are interested in the implementation being used, check out the http://labs.carrotsearch.com/randomizedtesting.html[RandomizedTesting webpage].
First, you need to include the testing dependency in your project, along with the Elasticsearch dependency you have already added. If you use maven and its `pom.xml` file, it looks like this
If your test is a well isolated unit test which doesn't need a running Elasticsearch cluster, you can use the `ESTestCase`. If you are testing lucene features, use `ESTestCase` and if you are testing concrete token streams, use the `ESTokenStreamTestCase` class. Those specific classes execute additional checks which ensure that no resources leaks are happening, after the test has run.
These kind of tests require firing up a whole cluster of nodes, before the tests can actually be run. Compared to unit tests they are obviously way more time consuming, but the test infrastructure tries to minimize the time cost by only restarting the whole cluster, if this is configured explicitly.
The class your tests have to inherit from is `ESIntegTestCase`. By inheriting from this class, you will no longer need to start Elasticsearch nodes manually in your test, although you might need to ensure that at least a certain number of nodes are up. The integration test behaviour can be configured heavily by specifying different system properties on test runs. See the `TESTING.asciidoc` documentation in the https://github.com/elastic/elasticsearch/blob/master/TESTING.asciidoc[source repository] for more information.
The number of shards used for indices created during integration tests is randomized between `1` and `10` unless overwritten upon index creation via index settings.
The rule of thumb is not to specify the number of shards unless needed, so that each test will use a different one all the time. Alternatively you can override the `numberOfShards()` method. The same applies to the `numberOfReplicas()` method.
The `InternalTestCluster` class is the heart of the cluster functionality in a randomized test and allows you to configure a specific setting or replay certain types of outages to check, how your custom code reacts.
If you want to ensure a certain configuration for the nodes, which are started as part of the `EsIntegTestCase`, you can override the `nodeSettings()` method
In order to execute any actions, you have to use a client. You can use the `ESIntegTestCase.client()` method to get back a random client. This client can be a `TransportClient` or a `NodeClient` - and usually you do not need to care as long as the action gets executed. There are several more methods for client selection inside of the `InternalTestCluster` class, which can be accessed using the `ESIntegTestCase.internalCluster()` method.
By default the tests are run with unique cluster per test suite. Of course all indices and templates are deleted between each test. However, sometimes you need to start a new cluster for each test - for example, if you load a certain plugin, but you do not want to load it for every test.
As Elasticsearch is using JUnit 4, using the `@Before` and `@After` annotations is not a problem. However you should keep in mind, that this does not have any effect in your cluster setup, as the cluster is already up and running when those methods are run. So in case you want to configure settings - like loading a plugin on node startup - before the node is actually running, you should overwrite the `nodePlugins()` method from the `ESIntegTestCase` class and return the plugin classes each node should load.
The code snippets you saw so far did not show any trace of randomized testing features, as they are carefully hidden under the hood. However when you are writing your own tests, you should make use of these features as well. Before starting with that, you should know, how to repeat a failed test with the same setup, how it failed. Luckily this is quite easy, as the whole mvn call is logged together with failed tests, which means you can simply copy and paste that line and run the test.
The next step is to convert your test using static test data into a test using randomized test data. The kind of data you could randomize varies a lot with the functionality you are testing against. Take a look at the following examples (note, that this list could go on for pages, as a distributed system has many, many moving parts):
* Searching for data using arbitrary UTF8 signs
* Changing your mapping configuration, index and field names with each run
* Changing your response sizes/configurable limits with each run
* Changing the number of shards/replicas when creating an index
So, how can you create random data. The most important thing to know is, that you never should instantiate your own `Random` instance, but use the one provided in the `RandomizedTest`, from which all Elasticsearch dependent test classes inherit from.
In addition, there are a couple of helper methods, allowing you to create random ASCII and Unicode strings, see methods beginning with `randomAscii`, `randomUnicode`, and `randomRealisticUnicode` in the random test class. The latter one tries to create more realistic unicode string by not being arbitrary random.
If you want to debug a specific problem with a specific random seed, you can use the `@Seed` annotation to configure a specific seed for a test. If you want to run a test more than once, instead of starting the whole test suite over and over again, you can use the `@Repeat` annotation with an arbitrary value. Each iteration than gets run with a different seed.
As many Elasticsearch tests are checking for a similar output, like the amount of hits or the first hit or special highlighting, a couple of predefined assertions have been created. Those have been put into the `ElasticsearchAssertions` class. There is also a specific geo assertions in `ElasticsearchGeoAssertions`.
