RateLimiter.java

@Test
    public void rateLimiterTest() {

        MockResponse mockResponse = new MockResponse()
                .setResponseCode(200)
                .addHeader("Content-Type", "application/json;charset=utf-8");

        //Resilience4J configuration for RateLimiter
        //Defining that only one request can happend in 100ms window
        RateLimiterConfig config = RateLimiterConfig.custom()
                .timeoutDuration(Duration.ofMillis(100))
                .limitRefreshPeriod(Duration.ofSeconds(1))
                .limitForPeriod(1)
                .build();

        // Create a RateLimiter
        RateLimiter rateLimiter = RateLimiter.of("books", config);
        
        //This only capture all the emmitted by the library
        this.captureEvents(rateLimiter.getEventPublisher());

        // Decorate your call to BackendService.doSomething()
        Supplier<String> restrictedSupplier = RateLimiter
                .decorateSupplier(rateLimiter, bookClient::findAll);

        //THis prepares the mock server to mock 2 requests
        this.enqueue(2, mockResponse);

        // Try.ofSupplier will execute the decorated function above
        Try<String> firstTry = Try.ofSupplier(restrictedSupplier);
      
        //First call will be successful
        Assertions.assertThat(firstTry.isSuccess()).isTrue();

        // Second call fails, because the call was executed inside a 100ms window
        Try<String> secondTry = Try.ofSupplier(restrictedSupplier);
        Assertions.assertThat(secondTry.isFailure()).isTrue();
        Assertions.assertThat(secondTry.getCause()).isInstanceOf(RequestNotPermitted.class);

        // Asserting that the first call was successful, and thhe second one failed
        Assertions.assertThat(this.events)
                .extracting(RateLimiterEvent::getEventType)
                .containsExactly(
                        RateLimiterEvent.Type.SUCCESSFUL_ACQUIRE,
                        RateLimiterEvent.Type.FAILED_ACQUIRE
                );
    }