1500d1f36d
A SubFlow (or SubSource) is not a Graph, it is an unfinished builder that accepts transformations. This allows us to capture the substreams’ transformations before materializing the flow, which will be very helpful in fully fusing all operators. Another change is that groupBy now requires a maxSubstreams parameter in order to bound its resource usage. In exchange the matching merge can be unbounded. This trades silent deadlock for explicit stream failure. This commit also changes all uses of Predef.identity to use `conforms` and removes the HTTP impl.util.identityFunc.
100 lines
4.6 KiB
ReStructuredText
100 lines
4.6 KiB
ReStructuredText
.. _stream-testkit-java:
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###############
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Testing streams
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###############
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Verifying behaviour of Akka Stream sources, flows and sinks can be done using
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various code patterns and libraries. Here we will discuss testing these
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elements using:
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- simple sources, sinks and flows;
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- sources and sinks in combination with :class:`TestProbe` from the :mod:`akka-testkit` module;
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- sources and sinks specifically crafted for writing tests from the :mod:`akka-stream-testkit` module.
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It is important to keep your data processing pipeline as separate sources,
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flows and sinks. This makes them easily testable by wiring them up to other
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sources or sinks, or some test harnesses that :mod:`akka-testkit` or
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:mod:`akka-stream-testkit` provide.
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Built in sources, sinks and combinators
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=======================================
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Testing a custom sink can be as simple as attaching a source that emits
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elements from a predefined collection, running a constructed test flow and
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asserting on the results that sink produced. Here is an example of a test for a
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sink:
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#strict-collection
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The same strategy can be applied for sources as well. In the next example we
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have a source that produces an infinite stream of elements. Such source can be
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tested by asserting that first arbitrary number of elements hold some
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condition. Here the ``grouped`` combinator and ``Sink.head`` are very useful.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#grouped-infinite
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When testing a flow we need to attach a source and a sink. As both stream ends
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are under our control, we can choose sources that tests various edge cases of
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the flow and sinks that ease assertions.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#folded-stream
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TestKit
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=======
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Akka Stream offers integration with Actors out of the box. This support can be
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used for writing stream tests that use familiar :class:`TestProbe` from the
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:mod:`akka-testkit` API.
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One of the more straightforward tests would be to materialize stream to a
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:class:`Future` and then use ``pipe`` pattern to pipe the result of that future
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to the probe.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#pipeto-testprobe
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Instead of materializing to a future, we can use a :class:`Sink.actorRef` that
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sends all incoming elements to the given :class:`ActorRef`. Now we can use
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assertion methods on :class:`TestProbe` and expect elements one by one as they
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arrive. We can also assert stream completion by expecting for
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``onCompleteMessage`` which was given to :class:`Sink.actorRef`.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#sink-actorref
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Similarly to :class:`Sink.actorRef` that provides control over received
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elements, we can use :class:`Source.actorRef` and have full control over
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elements to be sent.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#source-actorref
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Streams TestKit
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===============
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You may have noticed various code patterns that emerge when testing stream
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pipelines. Akka Stream has a separate :mod:`akka-stream-testkit` module that
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provides tools specifically for writing stream tests. This module comes with
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two main components that are :class:`TestSource` and :class:`TestSink` which
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provide sources and sinks that materialize to probes that allow fluent API.
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.. note::
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Be sure to add the module :mod:`akka-stream-testkit` to your dependencies.
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A sink returned by ``TestSink.probe`` allows manual control over demand and
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assertions over elements coming downstream.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#test-sink-probe
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A source returned by ``TestSource.probe`` can be used for asserting demand or
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controlling when stream is completed or ended with an error.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#test-source-probe
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You can also inject exceptions and test sink behaviour on error conditions.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#injecting-failure
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Test source and sink can be used together in combination when testing flows.
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.. includecode:: ../../../akka-samples/akka-docs-java-lambda/src/test/java/docs/stream/StreamTestKitDocTest.java#test-source-and-sink
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