@Test
    public void shouldNotUpdateStoreForLargerValue() {
        inputTopic.pipeInput("a", 42L);
        assertThat(store.get("a"), equalTo(42L));
        assertThat(outputTopic.readKeyValue(), equalTo(new KeyValue<>("a", 42L)));
        assertThat(outputTopic.isEmpty(), is(true));
    }
This is code sample in docs/streams/developer-guide/testing.html
streams/examples/src/test/java/org/apache/kafka/streams/examples/docs/DeveloperGuideTesting.java