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StopWatchTests: improve test cases #36028

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857e917
StopWatchTests: improve test cases
vincentstradiot Dec 15, 2025
496f2b8
StopWatchTests: improve test cases
vincentstradiot Dec 15, 2025
dfeed2c
StopWatchTests: improve test cases
vincentstradiot Dec 16, 2025
b7259fa
StopWatchTests: improve test cases
vincentstradiot Dec 16, 2025
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32 changes: 29 additions & 3 deletions spring-core/src/main/java/org/springframework/util/StopWatch.java
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Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,12 @@ public class StopWatch {
/** Total running time. */
private long totalTimeNanos;

/**
* The {@link NanoClock} used to compute execution times of tasks.
* <br/>
* Defaults to {@link System#nanoTime()}, other implementations can be injected for unit testing.
*/
private final NanoClock nanoClock;

/**
* Construct a new {@code StopWatch}.
Expand All @@ -92,9 +98,21 @@ public StopWatch() {
* @param id identifier for this stop watch
*/
public StopWatch(String id) {
this.id = id;
this(id, System::nanoTime);
}

/**
* Construct a new {@code StopWatch} with the given id.
* <p>The id is handy when we have output from multiple stop watches and need
* to distinguish between them.
* <p>Does not start any task.
* @param id identifier for this stop watch
* @param nanoClock the {@link NanoClock} used to compute execution times of tasks
*/
public StopWatch(String id, NanoClock nanoClock) {
this.id = id;
this.nanoClock = nanoClock;
}

/**
* Get the id of this {@code StopWatch}, as specified on construction.
Expand Down Expand Up @@ -141,7 +159,7 @@ public void start(String taskName) throws IllegalStateException {
throw new IllegalStateException("Can't start StopWatch: it's already running");
}
this.currentTaskName = taskName;
this.startTimeNanos = System.nanoTime();
this.startTimeNanos = nanoClock.nanoTime();
}

/**
Expand All @@ -155,7 +173,7 @@ public void stop() throws IllegalStateException {
if (this.currentTaskName == null) {
throw new IllegalStateException("Can't stop StopWatch: it's not running");
}
long lastTime = System.nanoTime() - this.startTimeNanos;
long lastTime = nanoClock.nanoTime() - this.startTimeNanos;
this.totalTimeNanos += lastTime;
this.lastTaskInfo = new TaskInfo(this.currentTaskName, lastTime);
if (this.taskList != null) {
Expand Down Expand Up @@ -389,6 +407,14 @@ public String toString() {
return sb.toString();
}

/**
* An abstraction of a clock that provides nanosecond precision and that can be used to compute relative times.
*/
public interface NanoClock {

long nanoTime();

}

/**
* Nested class to hold data about one task executed within the {@code StopWatch}.
Expand Down
69 changes: 36 additions & 33 deletions spring-core/src/test/java/org/springframework/util/StopWatchTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -16,13 +16,17 @@

package org.springframework.util;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import org.springframework.util.StopWatch.TaskInfo;

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
import static org.mockito.Mockito.when;

/**
* Tests for {@link StopWatch}.
Expand All @@ -31,19 +35,23 @@
* @author Juergen Hoeller
* @author Sam Brannen
*/
@ExtendWith(MockitoExtension.class)
class StopWatchTests {

private static final String ID = "myId";

private static final String name1 = "Task 1";
private static final String name2 = "Task 2";

private static final long duration1 = 200;
private static final long duration2 = 100;
// private static final long fudgeFactor = 100;
private StopWatch stopWatch;

private final StopWatch stopWatch = new StopWatch(ID);
@Mock
private StopWatch.NanoClock nanoClock;

@BeforeEach
void setUp() {
stopWatch = new StopWatch(ID, nanoClock);
}

@Test
void failureToStartBeforeGettingTimings() {
Expand All @@ -57,6 +65,8 @@ void failureToStartBeforeStop() {

@Test
void rejectsStartTwice() {
when(nanoClock.nanoTime()).thenAnswer(invocation -> System.nanoTime());

stopWatch.start();
assertThat(stopWatch.isRunning()).isTrue();
stopWatch.stop();
Expand All @@ -68,52 +78,46 @@ void rejectsStartTwice() {
}

@Test
void validUsage() throws Exception {
void validUsage() {
when(nanoClock.nanoTime())
.thenReturn(1_000_000_000L) // start task 1
.thenReturn(2_000_000_000L) // stop task 1 (duration = 1 second)
.thenReturn(3_000_000_000L) // start task 2
.thenReturn(5_123_456_789L); // stop task 2 (duration = 2.123456789 seconds)

assertThat(stopWatch.isRunning()).isFalse();

stopWatch.start(name1);
Thread.sleep(duration1);
assertThat(stopWatch.isRunning()).isTrue();
assertThat(stopWatch.currentTaskName()).isEqualTo(name1);
stopWatch.stop();
assertThat(stopWatch.isRunning()).isFalse();

/* Flaky StopWatch time assertions...
assertThat(stopWatch.getLastTaskTimeNanos())
assertThat(stopWatch.lastTaskInfo().getTimeNanos())
.as("last task time in nanoseconds for task #1")
.isGreaterThanOrEqualTo(TimeUnit.MILLISECONDS.toNanos(duration1 - fudgeFactor))
.isLessThanOrEqualTo(TimeUnit.MILLISECONDS.toNanos(duration1 + fudgeFactor));
.isEqualTo(1_000_000_000L);
assertThat(stopWatch.getTotalTimeMillis())
.as("total time in milliseconds for task #1")
.isGreaterThanOrEqualTo(duration1 - fudgeFactor)
.isLessThanOrEqualTo(duration1 + fudgeFactor);
.as("total time in milliseconds")
.isEqualTo(1_000L);
assertThat(stopWatch.getTotalTimeSeconds())
.as("total time in seconds for task #1")
.isGreaterThanOrEqualTo((duration1 - fudgeFactor) / 1000.0)
.isLessThanOrEqualTo((duration1 + fudgeFactor) / 1000.0);
*/
.as("total time in seconds")
.isEqualTo(1.0);

stopWatch.start(name2);
Thread.sleep(duration2);
assertThat(stopWatch.isRunning()).isTrue();
assertThat(stopWatch.currentTaskName()).isEqualTo(name2);
stopWatch.stop();
assertThat(stopWatch.isRunning()).isFalse();

/* Flaky StopWatch time assertions...
assertThat(stopWatch.getLastTaskTimeNanos())
assertThat(stopWatch.lastTaskInfo().getTimeNanos())
.as("last task time in nanoseconds for task #2")
.isGreaterThanOrEqualTo(TimeUnit.MILLISECONDS.toNanos(duration2))
.isLessThanOrEqualTo(TimeUnit.MILLISECONDS.toNanos(duration2 + fudgeFactor));
.isEqualTo(2_123_456_789L);
assertThat(stopWatch.getTotalTimeMillis())
.as("total time in milliseconds for tasks #1 and #2")
.isGreaterThanOrEqualTo(duration1 + duration2 - fudgeFactor)
.isLessThanOrEqualTo(duration1 + duration2 + fudgeFactor);
.as("total time in milliseconds")
.isEqualTo(3_123L);
assertThat(stopWatch.getTotalTimeSeconds())
.as("total time in seconds for task #2")
.isGreaterThanOrEqualTo((duration1 + duration2 - fudgeFactor) / 1000.0)
.isLessThanOrEqualTo((duration1 + duration2 + fudgeFactor) / 1000.0);
*/
.as("total time in seconds")
.isEqualTo(3.123456789);

assertThat(stopWatch.getTaskCount()).isEqualTo(2);
assertThat(stopWatch.prettyPrint()).contains(name1, name2);
Expand All @@ -123,16 +127,15 @@ void validUsage() throws Exception {
}

@Test
void validUsageDoesNotKeepTaskList() throws Exception {
void validUsageDoesNotKeepTaskList() {
when(nanoClock.nanoTime()).thenAnswer(invocation -> System.nanoTime());
stopWatch.setKeepTaskList(false);

stopWatch.start(name1);
Thread.sleep(duration1);
assertThat(stopWatch.currentTaskName()).isEqualTo(name1);
stopWatch.stop();

stopWatch.start(name2);
Thread.sleep(duration2);
assertThat(stopWatch.currentTaskName()).isEqualTo(name2);
stopWatch.stop();

Expand Down