Merge pull request #3955 from iaforek/master

BAEL-1648 - Measure Time Elapsed in Java

core-java-8/src/test/java/com/baeldung/time/ElapsedTimeUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.time;
+
+import static org.junit.Assert.assertEquals;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.commons.lang3.time.StopWatch;
+import org.junit.Test;
+
+public class ElapsedTimeUnitTest {
+
+    @Test
+    public void givenRunningTask_whenMeasuringTimeWithCurrentTimeMillis_thenGetElapsedTime() throws InterruptedException {
+        long start = System.currentTimeMillis();
+        
+        simulateRunningTask();
+        
+        long finish = System.currentTimeMillis();
+        
+        long timeElapsed = finish - start;
+        
+        assertEquals(true, (2000L <= timeElapsed) && (timeElapsed <= 3000L));
+    }
+    
+    @Test
+    public void giveRunningTask_whenMeasuringTimeWithNanoTime_thenGetElapsedTime() throws InterruptedException {
+        long start = System.nanoTime();
+        
+        simulateRunningTask();
+        
+        long finish = System.nanoTime();
+        
+        long timeElapsed = finish - start;
+        
+        assertEquals(true, (2000000000L <= timeElapsed) && (timeElapsed <= 3000000000L));
+    }
+    
+    @Test
+    public void givenRunningTask_whenMeasuringTimeWithStopWatch_thenGetElapsedTime() throws InterruptedException {
+        StopWatch watch = new StopWatch();        
+        watch.start();
+
+        simulateRunningTask();
+        
+        watch.stop();
+        
+        long timeElapsed = watch.getTime();
+        
+        assertEquals(true, (2000L <= timeElapsed) && (timeElapsed <= 3000L));
+    }
+    
+    @Test
+    public void givenRunningTask_whenMeasuringTimeWithInstantClass_thenGetElapsedTime() throws InterruptedException {
+        Instant start = Instant.now();
+        
+        simulateRunningTask();
+        
+        Instant finish = Instant.now();
+        
+        long timeElapsed = Duration.between(start, finish).toMillis();
+        
+        assertEquals(true, (2000L <= timeElapsed) && (timeElapsed <= 3000L));
+    }
+    
+    /**
+     * Simulate task running for 2.5 seconds.
+     * 
+     * @throws InterruptedException
+     */
+    private static void simulateRunningTask() throws InterruptedException {
+        TimeUnit.MILLISECONDS.sleep(2500); // 2.5 seconds
+
+    } 
+}