@Override
    public File stateDir() {
        return Objects.requireNonNull(
            stateDir,
            "The stateDir constructor argument was needed (probably for a state store) but not supplied. " +
                "You can either reconfigure your test so that it doesn't need access to the disk " +
                "(such as using an in-memory store), or use the full MockProcessorContext constructor to supply " +
                "a non-null stateDir argument."
        );
    }
Create a {@link MockProcessorContext} with a specified taskId and null stateDir.

@param config   a {@link Properties} object, used to configure the context and the processor.
@param taskId   a {@link TaskId}, which the context makes available via {@link MockProcessorContext#taskId()}.
@param stateDir a {@link File}, which the context makes available viw {@link MockProcessorContext#stateDir()}.
streams/test-utils/src/main/java/org/apache/kafka/streams/processor/api/MockProcessorContext.java