private WindowBytesStoreSupplier buildWindowBytesStoreSupplier(final String name,
                                                                   final long retentionPeriod,
                                                                   final long windowSize,
                                                                   final boolean retainDuplicates) {
        return  Stores.inMemoryWindowStore(name,
                                           Duration.ofMillis(retentionPeriod),
                                           Duration.ofMillis(windowSize),
                                           retainDuplicates);
    }
This test is testing something internal to [[KStreamKStreamJoin]], so we had to setup low-level api manually.
streams/src/test/java/org/apache/kafka/streams/kstream/internals/KStreamKStreamJoinTest.java