Tests in MetricsIntegrationTests are non idempotent

[SaaiVenkat]

Issue

• The tests in org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsIntegrationTests, specifically requestMappingIsInstrumented() and restTemplateIsInstrumented() are not idempotent, since they pollute the state registry
• This might fail future tests that share the same state similar to CloudFoundry endpoint integration tests are order dependent #38363
• AssertionFailedError log when restTemplateIsInstrumented was run twice in the same JVM

org.opentest4j.AssertionFailedError: 
expected: 1L
 but was: 2L
	at [email protected]/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at [email protected]/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
	at [email protected]/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at [email protected]/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at app//org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsIntegrationTests.restTemplateIsInstrumented(MetricsIntegrationTests.java:111)

• AssertionFailedError log when requestMappingIsInstrumented was run twice in the same JVM

org.awaitility.core.ConditionTimeoutException: Assertion condition defined as a org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsIntegrationTests 
expected: 1L
 but was: 2L within 5 seconds.
	at app//org.awaitility.core.ConditionAwaiter.await(ConditionAwaiter.java:167)
	at app//org.awaitility.core.AssertionCondition.await(AssertionCondition.java:119)
	at app//org.awaitility.core.AssertionCondition.await(AssertionCondition.java:31)
	at app//org.awaitility.core.ConditionFactory.until(ConditionFactory.java:985)
	at app//org.awaitility.core.ConditionFactory.untilAsserted(ConditionFactory.java:769)
	at app//org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsIntegrationTests.requestMappingIsInstrumented(MetricsIntegrationTests.java:118)

Cause

• Each of the above mentioned tests pollutes the shared state registry across test runs, which causes the second test run to fail for assertions on the registry's timer count

• spring-boot/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/test/MetricsIntegrationTests.java

  Line 110 in 212b80a

  assertThat(this.registry.get("http.client.requests").timer().count()).isOne();

• spring-boot/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/test/MetricsIntegrationTests.java

  Line 117 in 212b80a

  .untilAsserted(() -> assertThat(this.registry.get("http.server.requests").timer().count()).isOne());

• It's better to clear this polluted state preemptively, so that future tests that use the same state will not fail.

Steps to reproduce

• Run each of the above mentioned test twice in the same JVM using @RepeatedTest(2)

Proposed Fix

• Since the registry's timer state is polluted across different runs, I have reset the registry state before each test run
• Added a setUp() with @BeforeEach where the registry state is cleared using this.registry.clear()

[mhalbritter]

Thanks for the analysis! I've fixed that.