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Status

Current state: "Under Discussion"

Discussion thread: here 

JIRA: KAFKA-6460

Motivation

This is for adding mock testing support for StateStore, StoreBuilder, StoreSupplier and other store related components which are used in Streams unit testing.

We'd like to use mocks for different types of state stores: KV, window, session - that can be used to record the number of expected put / get calls used in the DSL operator unit testing. These will provide convenience for developers when they are writing unit test for Kafka stream and other related modules.

For example, in the current streams/TopologyTest.java:

public class TopologyTest {

    private final StoreBuilder storeBuilder = EasyMock.createNiceMock(StoreBuilder.class);
    private final KeyValueStoreBuilder globalStoreBuilder = EasyMock.createNiceMock(KeyValueStoreBuilder.class);
    private final Topology topology = new Topology();    
...

	@Test
    public void shouldFailIfSinkIsParent() {
        topology.addSource("source", "topic-1");
        topology.addSink("sink-1", "topic-2", "source");
        try {
            topology.addSink("sink-2", "topic-3", "sink-1");
            fail("Should throw TopologyException for using sink as parent");
        } catch (final TopologyException expected) { }
    }

    @Test(expected = TopologyException.class)
    public void shouldNotAllowToAddStateStoreToNonExistingProcessor() {
        mockStoreBuilder();
        EasyMock.replay(storeBuilder);
        topology.addStateStore(storeBuilder, "no-such-processor");
    }

    @Test
    public void shouldNotAllowToAddStateStoreToSource() {
        mockStoreBuilder();
        EasyMock.replay(storeBuilder);
        topology.addSource("source-1", "topic-1");
        try {
            topology.addStateStore(storeBuilder, "source-1");
            fail("Should have thrown TopologyException for adding store to source node");
        } catch (final TopologyException expected) { }
    }

	private void mockStoreBuilder() {
        EasyMock.expect(storeBuilder.name()).andReturn("store").anyTimes();
        EasyMock.expect(storeBuilder.logConfig()).andReturn(Collections.emptyMap());
        EasyMock.expect(storeBuilder.loggingEnabled()).andReturn(false);
    }
}

One of the goal is to replace the in-test vanilla mockStoreBuilder with a more general purpose mockStoreBuilder class, which simplify writing unit test and can be reuse later.

After the improvements, we will replace the easyMock StoreBuilder with our mockStoreBuilder.

public class TopologyTest {

    private final StoreBuilder storeBuilder = EasyMock.createNiceMock(StoreBuilder.class);
    private final Topology topology = new Topology();
    private final MockStoreFactory mockStoreFactory = new MockStoreFactory<>();
    private final KeyValueStoreBuilder keyValueStoreBuilder = mockStoreFactory.createKeyValueStoreBuilder(
            Stores.inMemoryKeyValueStore("store"),
            Serdes.Bytes(),
            Serdes.Bytes(),
            false);

...
    @Test(expected = TopologyException.class)
    public void shouldNotAllowToAddStateStoreToNonExistingProcessor() {
        topology.addStateStore(keyValueStoreBuilder, "no-such-processor");
    }
}


Public Interfaces

We add some new classes to the kafka-streams-test-utils under internal.


We will provide a MockStoreFactory to generate mock store builders, I will use the KeyValueStoreBuilder as an example. Window and Session will have a similar structure.

The developers/users can provide their own store as the backend storage, and their own Serde of choice. For example, for simple testing, they can just use an InMemoryKeyValueStore.

package org.apache.kafka.streams.internals;

public class MockStoreFactory<K, V> {

    public final Map<String, StoreBuilder> stateStores = new LinkedHashMap<>();

    public MockStoreFactory () {
    }

    public KeyValueStoreBuilder createKeyValueStoreBuilder(KeyValueBytesStoreSupplier keyValueBytesStoreSupplier,
                                                           final Serde<K> keySerde,
                                                           final Serde<V> valueSerde,
                                                           boolean persistent){
		String storeName = keyValueBytesStoreSupplier.name();
        stateStores.put(storeName, new MockKeyValueStoreBuilder<>(keyValueBytesStoreSupplier, keySerde, valueSerde, persistent));
        return (KeyValueStoreBuilder)stateStores.get(storeName);
    }

	public WindowStoreBuilder createWindowStoreBuilder(KeyValueBytesStoreSupplier keyValueBytesStoreSupplier,
                                                           final Serde<K> keySerde,
                                                           final Serde<V> valueSerde,
                                                           final Time time){
	...
	}

	public SessionStoreBuilder createSessionStoreBuilder(KeyValueBytesStoreSupplier keyValueBytesStoreSupplier,
                                                           final Serde<K> keySerde,
                                                           final Serde<V> valueSerde,
                                                           final Time time){
	...
	}

    public StoreBuilder getStore(String storeName) {
        return stateStores.get(storeName);
    }
}


Each Store builder will have a build method:

package org.apache.kafka.streams.internals;

import org.apache.kafka.common.serialization.Serde;

import org.apache.kafka.streams.MockTime;
import org.apache.kafka.streams.state.KeyValueBytesStoreSupplier;
import org.apache.kafka.streams.state.KeyValueStore;
import org.apache.kafka.streams.state.internals.AbstractStoreBuilder;



public class MockKeyValueStoreBuilder<K, V> extends AbstractStoreBuilder<K, V, KeyValueStore> {

    private final boolean persistent;
    private final KeyValueBytesStoreSupplier storeSupplier;

    public MockKeyValueStoreBuilder(final KeyValueBytesStoreSupplier storeSupplier,
                                    final Serde<K> keySerde,
                                    final Serde<V> valueSerde,
                                    final boolean persistent) {
        super(storeSupplier.name(), keySerde, valueSerde, new MockTime(0));
        this.persistent = persistent;
        this.storeSupplier = storeSupplier;

    }

    @Override
    public KeyValueStore build() {
        return new MockKeyValueStore<>(name, storeSupplier.get(), persistent);
    }
}


Then in the store, we will build a wrapper around the provided backend store. We will capture each get/put/delete call, the user can write tests accordingly. We will also track if the store has been flushed or closed.

package org.apache.kafka.streams.internals;

import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.processor.ProcessorContext;
import org.apache.kafka.streams.processor.StateRestoreCallback;
import org.apache.kafka.streams.processor.StateStore;
import org.apache.kafka.streams.state.KeyValueIterator;
import org.apache.kafka.streams.state.KeyValueStore;

import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

public class MockKeyValueStore<K, V> implements KeyValueStore<K, V>  {
    // keep a global counter of flushes and a local reference to which store had which
    // flush, so we can reason about the order in which stores get flushed.
    private static final AtomicInteger GLOBAL_FLUSH_COUNTER = new AtomicInteger(0);
    private final AtomicInteger instanceLastFlushCount = new AtomicInteger(-1);
    private final String name;
    private final boolean persistent;

    public boolean initialized = false;
    public boolean flushed = false;
    public boolean closed = true;

    public final List<KeyValue<K, V>> capturedPutCalls = new LinkedList<>();
    public final List<KeyValue<K, V>> capturedGetCalls = new LinkedList<>();
    public final List<KeyValue<K, V>> capturedDeleteCalls = new LinkedList<>();

    public final KeyValueStore<K, V> innerKeyValueStore;

    public MockKeyValueStore(final String name,
                             final KeyValueStore<K, V> innerKeyValueStore,
                             final boolean persistent) {
        this.name = name;
        this.innerKeyValueStore = innerKeyValueStore;
        this.persistent = persistent;

    }

    @Override
    public String name() {
        return name;
    }

    @Override
    public void init(final ProcessorContext context,
                     final StateStore root) {
        context.register(root, stateRestoreCallback);
        initialized = true;
        closed = false;
    }

    @Override
    public void flush() {
        instanceLastFlushCount.set(GLOBAL_FLUSH_COUNTER.getAndIncrement());
        innerKeyValueStore.flush();
        flushed = true;
    }

    public int getLastFlushCount() {
        return instanceLastFlushCount.get();
    }

    @Override
    public void close() {
        innerKeyValueStore.close();
        closed = true;
    }

    @Override
    public boolean persistent() {
        return persistent;
    }

    @Override
    public boolean isOpen() {
        return !closed;
    }

    public final StateRestoreCallback stateRestoreCallback = new StateRestoreCallback() {

        @Override
        public void restore(final byte[] key,
                            final byte[] value) {
        }
    };

    @Override
    public void put(final K key, final V value) {
        capturedPutCalls.add(new KeyValue<>(key, value));
        innerKeyValueStore.put(key, value);
    }

    @Override
    public V putIfAbsent(final K key, final V value) {
        final V originalValue = get(key);
        if (originalValue == null) {
            put(key, value);
            capturedPutCalls.add(new KeyValue<>(key, value));
        }
        return originalValue;
    }

    @Override
    public V delete(final K key) {
        V value = innerKeyValueStore.delete(key);
        capturedDeleteCalls.add(new KeyValue<>(key, value));
        return value;
    }

    @Override
    public void putAll(final List<KeyValue<K, V>> entries) {
        for (final KeyValue<K, V> entry : entries) {
            put(entry.key, entry.value);
            capturedPutCalls.add(entry);
        }
    }

    @Override
    public V get(final K key) {
        V value = innerKeyValueStore.get(key);
        capturedGetCalls.add(new KeyValue<>(key, value));
        return value;
    }

    @Override
    public KeyValueIterator<K,V> range(final K from, final K to) {
        return innerKeyValueStore.range(from, to);
    }

    @Override
    public KeyValueIterator<K,V>  all() {
        return innerKeyValueStore.all();
    }

    @Override
    public long approximateNumEntries() {
        return innerKeyValueStore.approximateNumEntries();
    }
}


Proposed Changes

I proposed to add:

  1. a MockStoreFactory class to produce mock state store builders.
  2. A mock StateStoreBuilder class for KV, Session and Window.
  3. A mock StateStore class for KV, Session and Window with tracking.

Compatibility, Deprecation, and Migration Plan

Until we are refactoring with these new MockStateStores, there shouldn't be any compatibility issues. But the next phase should be refactoring, including:

1) Remove and refactor redundant MockStores (i.e. org.apache.kafka.test.MockKeyValueStore)

2) Examine the current tests (i.e. org.apache.kafka.streams.TopologyTest and refactor the testing code logics with the new MockStateStores.

Rejected Alternatives

  1. Using the current EasyMock implementation. There is no strong argument against the current EasyMock implementation, it is easy to use and lightweight. The main argument for this KIP is to write better tests with a in-house mock state store support.



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