Beal 1006 rate limmiter (#2224)

* BAEL-1006 rate limiter tests

* BAEL-1006 simpler example

guava/src/test/java/org/baeldung/guava/RateLimiterUnitTest.java

@@ -0,0 +1,81 @@
+package org.baeldung.guava;
+
+
+import com.google.common.util.concurrent.RateLimiter;
+import org.junit.Test;
+
+import java.time.ZonedDateTime;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.IntStream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class RateLimiterUnitTest {
+
+    @Test
+    public void givenLimitedResource_whenUseRateLimiter_thenShouldLimitPermits() {
+        //given
+        RateLimiter rateLimiter = RateLimiter.create(100);
+
+        //when
+        long startTime = ZonedDateTime.now().getSecond();
+        IntStream.range(0, 1000).forEach(i -> {
+            rateLimiter.acquire();
+            doSomeLimitedOperation();
+        });
+        long elapsedTimeSeconds = ZonedDateTime.now().getSecond() - startTime;
+
+        //then
+        assertThat(elapsedTimeSeconds >= 10);
+    }
+
+    @Test
+    public void givenLimitedResource_whenRequestTwice_thenShouldPermitWithoutBlocking() {
+        //given
+        RateLimiter rateLimiter = RateLimiter.create(2);
+
+        //when
+        long startTime = ZonedDateTime.now().getSecond();
+        rateLimiter.acquire(1);
+        doSomeLimitedOperation();
+        rateLimiter.acquire(1);
+        doSomeLimitedOperation();
+        long elapsedTimeSeconds = ZonedDateTime.now().getSecond() - startTime;
+
+        //then
+        assertThat(elapsedTimeSeconds <= 1);
+    }
+
+    @Test
+    public void givenLimitedResource_whenRequestOnce_thenShouldPermitWithoutBlocking() {
+        //given
+        RateLimiter rateLimiter = RateLimiter.create(100);
+
+        //when
+        long startTime = ZonedDateTime.now().getSecond();
+        rateLimiter.acquire(100);
+        doSomeLimitedOperation();
+        long elapsedTimeSeconds = ZonedDateTime.now().getSecond() - startTime;
+
+        //then
+        assertThat(elapsedTimeSeconds <= 1);
+    }
+
+    @Test
+    public void givenLimitedResource_whenTryAcquire_shouldNotBlockIndefinitely() {
+        //given
+        RateLimiter rateLimiter = RateLimiter.create(1);
+
+        //when
+        boolean result = rateLimiter.tryAcquire(2, 1, TimeUnit.SECONDS);
+
+        //then
+        assertThat(result).isFalse();
+
+    }
+
+    private void doSomeLimitedOperation() {
+        //some computing
+    }
+
+}