public static <T> void assertFutureFirstEquals(final T expected, final StreamRecorder<T> responseObserver,
            final int timeout, final TimeUnit timeoutUnit) {
        assertFutureFirstEquals(expected, responseObserver, UnaryOperator.identity(), timeout, timeoutUnit);
    }
Asserts that the first value in the {@link StreamRecorder} equals the expected value.

@param <T> The type of the observer's content.
@param expected The expected content.
@param responseObserver The observer to check for the expected content.
@param timeout The maximum time to wait for the result.
@param timeoutUnit The time unit of the {@code timeout} argument.
tests/src/test/java/net/devh/boot/grpc/test/util/GrpcAssertions.java