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

@param <T> The type of the unwrapped/expected content.
@param <R> The type of the observer's content.
@param expected The expected content.
@param responseObserver The observer to check for the expected content.
@param unwrapper The function used to extract the 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