[FLINK-11463] Rework end-to-end tests in Java - ASF JIRA

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Type: New Feature
Status: Open
Priority: Not a Priority
Resolution: Unresolved
Affects Version/s: None
Fix Version/s: None
Component/s: Test Infrastructure
Labels:

Description

This is the (long-term) umbrella issue for reworking our end-to-tests in Java on top of a new set of utilities.

Below are some areas where problems have been identified that I want to address with a prototype soon. This prototype primarily aims to introduce certain patterns to be built upon in the future.

Environments

Problem

Our current tests directly work against flink-dist and setup local clusters with/-out HA. Similar issues apply to Kafka and ElasticSearch.
This prevents us from re-using tests for other environments (Yarn, Docker) and distributed settings.

We also frequently have issues with cleaning up resources as it is the responsibility of the test itself.

Proposal

Introduce a common interface for a given resource type (i.e. Flink, Kafka) that tests will work against.
These resources should be implemented as jUnit external resources to allow reasonable life-cycle management.

Tests get access to an instance of this resource through a factory method.

Each resource implementation has a dedicated factory that is loaded with a ServiceLoader. Factories evaluate system-properties to determine whether the implementation should be loaded, and then optionally configure the resource.

Example:

public interface FlinkResource {
	... common methods ...

/**
	 * Returns the configured FlinkResource implementation, or a {@link LocalStandaloneFlinkResource} if none is configured.
	 *
	 * @return configured FlinkResource, or {@link LocalStandaloneFlinkResource} is none is configured
	 */
	FlinkResource get() {
		// load factories
		// evaluate system properties
		// return instance
	}
}

public interface FlinkResourceFactory {

	/**
	 * Returns a {@link FlinkResource} instance. If the instance could not be instantiated (for example, because a
	 * mandatory parameter was missing), then an empty {@link Optional} should be returned.
	 *
	 * @return FlinkResource instance, or an empty Optional if the instance could not be instantiated
	 */
	Optional<FlinkResource> create();
}

As example, running mvn verify -De2e.flink.mode=localStandalone could load a FlinkResource that sets up a local standalone cluster, while for mvn verify -De2e.flink.mode=distributedStandalone -De2e.flink.hosts=... it would connect to the given host and setup a distributed cluster.

Tests are not required to work against the common interface, and may be hard-wired to run against specific implementations. Simply put, the resource implementations should be public.

Future considerations

The factory method may be extended to allow tests to specify a set of conditions that must be fulfilled, for example HA to be enabled. If this requirement cannot be fulfilled the test should be skipped.

Split Management

Problem

End-to-end tests are run in separate cron-<version>-e2e branches. To accommodate the Travis time limits we run a total of 6 jobs each covering a subset of the tests.
These so-called splits are currently managed in the respective branches, and not on master/release branches.

This is a rather hidden detail that not everyone is aware of, nor is it easily discoverable. This has resulted several times in newly added tests not actually being run. Furthermore, if the arguments for tests are modified these changes have to be replicated to each branch.

Proposal

Use jUnit Categories to assign each test explicitly to one of the Travis jobs.

@Category(TravisGroup1.class)
public class MyTestRunningInTheFirstJob {
	...
}

It's a bit on the nose but a rather simple solution.

A given group of tests could be executed by running mvn verify -Dcategories="org.apache.flink.tests.util.TravisGroup1".
All tests can be executed by running mvn verify -Dcategories=""org.apache.flink.tests.util.TravisGroup1""

Future considerations

Tests may furthermore be categorized based on what they are testing (e.g. "Metrics", "Checkpointing", "Kafka") to allow running a certain subset of tests quickly.

Caching of downloaded artifacts

Problem

Several tests download archives for setting up systems, like Kafka of Elasticsearch. We currently do not cache downloads in any way, resulting in less stable tests (as mirrors aren't always available) and overall increased test duration (since the downloads at times are quite slow). The duration issue becomes especially apparent when running tests in a loop for debugging or release-testing purposes.
Finally, it also puts unnecessary strain on the download mirrors.

Proposal

Add a DownloadCache interface with a single Path getOrDownload(String url, Path targetDir) method.
Access to and loading of implementations are handled like resources (see above).

The caching behavior is implementation-dependent.

A reasonable implementation should allow files may be cached in a user-provided directory, with an optional time-to-live for long-term setups.