Refactor ExponentialBackoffManager and TestLinearBackoffManager Tests to Remove Thread.sleep(). (#495)

This commit enhances the ExponentialBackoffManager and TestLinearBackoffManager unit tests by replacing the use of Thread.sleep() with direct manipulation of internal state to simulate the cooldown period. This change improves test reliability and ensures consistent behavior in resource-constrained environments.

httpclient5/src/test/java/org/apache/hc/client5/http/impl/classic/TestExponentialBackoffManager.java

@@ -36,6 +36,9 @@ import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.time.Instant;
+import java.util.Map;
+
 public class TestExponentialBackoffManager {
 
     private ExponentialBackoffManager impl;
@@ -62,14 +65,18 @@ public class TestExponentialBackoffManager {
     }
 
     @Test
-    public void exponentialGrowthRateIsConfigurable() throws InterruptedException {
+    public void exponentialGrowthRateIsConfigurable() {
         final int customCoolDownMs = 500;
         connPerRoute.setMaxPerRoute(route, 4);
         impl.setBackoffFactor(0.5);
         impl.setCoolDown(TimeValue.ofMilliseconds(customCoolDownMs));
         impl.backOff(route);
         assertEquals(2, connPerRoute.getMaxPerRoute(route));
-        Thread.sleep(customCoolDownMs + 100); // Sleep for a slightly longer than the custom cooldown period
+
+        // Manipulate lastRouteBackoffs to simulate that enough time has passed for the cooldown period
+        final Map<HttpRoute, Instant> lastRouteBackoffs = impl.getLastRouteBackoffs();
+        lastRouteBackoffs.put(route, Instant.now().minusMillis(customCoolDownMs + 1));
+
         impl.backOff(route);
         assertEquals(1, connPerRoute.getMaxPerRoute(route));
     }
@@ -84,41 +91,62 @@ public class TestExponentialBackoffManager {
     }
 
     @Test
-    public void backoffDoesNotAdjustDuringCoolDownPeriod() throws InterruptedException {
+    public void backoffDoesNotAdjustDuringCoolDownPeriod() {
         connPerRoute.setMaxPerRoute(route, 4);
         impl.backOff(route);
         final long max = connPerRoute.getMaxPerRoute(route);
-        Thread.sleep(1); // Sleep for 1 ms
+
+        // Manipulate lastRouteBackoffs to simulate that not enough time has passed for the cooldown period
+        final Map<HttpRoute, Instant> lastRouteBackoffs = impl.getLastRouteBackoffs();
+        lastRouteBackoffs.put(route, Instant.now().minusMillis(10));
+
+        // Perform another backoff
         impl.backOff(route);
         assertEquals(max, connPerRoute.getMaxPerRoute(route));
     }
 
     @Test
-    public void backoffStillAdjustsAfterCoolDownPeriod() throws InterruptedException {
+    public void backoffStillAdjustsAfterCoolDownPeriod() {
         connPerRoute.setMaxPerRoute(route, 8);
         impl.backOff(route);
         final long max = connPerRoute.getMaxPerRoute(route);
-        Thread.sleep(DEFAULT_COOL_DOWN_MS + 1); // Sleep for cooldown period + 1 ms
+
+        // Manipulate lastRouteBackoffs to simulate that enough time has passed for the cooldown period
+        final Map<HttpRoute, Instant> lastRouteBackoffs = impl.getLastRouteBackoffs();
+        lastRouteBackoffs.put(route, Instant.now().minusMillis(DEFAULT_COOL_DOWN_MS + 1));
+
+        // Perform another backoff
         impl.backOff(route);
+
+        // Assert that the max connections have decreased
         assertTrue(max == 1 || max > connPerRoute.getMaxPerRoute(route));
     }
 
+
     @Test
-    public void probeDoesNotAdjustDuringCooldownPeriod() throws InterruptedException {
+    public void probeDoesNotAdjustDuringCooldownPeriod() {
         connPerRoute.setMaxPerRoute(route, 4);
         impl.probe(route);
         final long max = connPerRoute.getMaxPerRoute(route);
-        Thread.sleep(1); // Sleep for 1 ms
+
+        // Manipulate lastRouteProbes to simulate that not enough time has passed for the cooldown period
+        final Map<HttpRoute, Instant> lastRouteProbes = impl.getLastRouteProbes();
+        lastRouteProbes.put(route, Instant.now().minusMillis(0));
+
         impl.probe(route);
         assertEquals(max, connPerRoute.getMaxPerRoute(route));
     }
 
     @Test
-    public void probeStillAdjustsAfterCoolDownPeriod() throws InterruptedException {
+    public void probeStillAdjustsAfterCoolDownPeriod() {
         connPerRoute.setMaxPerRoute(route, 8);
         impl.probe(route);
         final long max = connPerRoute.getMaxPerRoute(route);
-        Thread.sleep(DEFAULT_COOL_DOWN_MS + 1); // Sleep for cooldown period + 1 ms
+
+        // Manipulate lastRouteProbes to simulate that enough time has passed for the cooldown period
+        final Map<HttpRoute, Instant> lastRouteProbes = impl.getLastRouteProbes();
+        lastRouteProbes.put(route, Instant.now().minusMillis(DEFAULT_COOL_DOWN_MS + 1));
+
         impl.probe(route);
         assertTrue(max < connPerRoute.getMaxPerRoute(route));
     }
@@ -126,7 +154,6 @@ public class TestExponentialBackoffManager {
     @Test
     public void willBackoffImmediatelyEvenAfterAProbe() {
         connPerRoute.setMaxPerRoute(route, 8);
-        final long now = System.currentTimeMillis();
         impl.probe(route);
         final long max = connPerRoute.getMaxPerRoute(route);
         impl.backOff(route);
@@ -134,22 +161,23 @@ public class TestExponentialBackoffManager {
     }
 
     @Test
-    public void coolDownPeriodIsConfigurable() throws InterruptedException {
+    public void coolDownPeriodIsConfigurable() {
         final long cd = 500; // Fixed cooldown period of 500 milliseconds
         impl.setCoolDown(TimeValue.ofMilliseconds(cd));
-
+        connPerRoute.setMaxPerRoute(route, 4);
-        // Sleep for a short duration before starting the test to reduce potential timing issues
-        Thread.sleep(100);
-
-        // Probe and check if the connection count remains the same during the cooldown period
         impl.probe(route);
         final int max0 = connPerRoute.getMaxPerRoute(route);
-        Thread.sleep(cd / 2); // Sleep for half the cooldown period
+
+        // Manipulate lastRouteProbes to simulate that not enough time has passed for the cooldown period
+        final Map<HttpRoute, Instant> lastRouteProbes = impl.getLastRouteProbes();
+        lastRouteProbes.put(route, Instant.now().minusMillis(cd / 2));
+
         impl.probe(route);
         assertEquals(max0, connPerRoute.getMaxPerRoute(route));
 
-        // Probe and check if the connection count increases after the cooldown period
+        // Manipulate lastRouteProbes again to simulate that enough time has passed for the cooldown period
-        Thread.sleep(cd / 2 + 1); // Sleep for the remaining half of the cooldown period + 1 ms
+        lastRouteProbes.put(route, Instant.now().minusMillis(cd + 1));
+
         impl.probe(route);
         assertTrue(max0 < connPerRoute.getMaxPerRoute(route));
     }