Recently I had the need of doing some integration tests that include components declared as Beans which generate traces and I had some drawbacks. I would like to share them with you and if you agree, I could contribute to the repo with the solution I found. (Not sure if this is the right repo, as micrometer-tracing does not include Spring Boot. If it is not, I would appreciate your opinion and the redirection to the right repo).

On one hand, I tried the approach of using the micrometer-tracing-test injecting the SimpleTracer as a bean, so the spring components make use of it. But I realized that some components are not executed. For example:

• Compoments used by the vendor implementation like io.micrometer.tracing.otel.bridge.Slf4JBaggageEventListener (otel is the implementation which I am using at the project) or io.opentelemetry.sdk.trace.SpanProcessor. But also
• Components from the micrometer api like io.micrometer.tracing.exporter.SpanFilter that although they are generic, they are called by the implementation bridge. (For example from io.micrometer.tracing.otel.bridge.CompositeSpanExporter).

On the other hand, I tried to use the micrometer-tracing-integration-test but I could not publish the Tracer created there as a bean.

Having said that, I would suggest to have some tracing testing tool which integrates with Spring Boot and can make test like the following:

@SpringBootTest(classes = TracingTestWithSBTestConfig.class)
@TracingTest //JunitExtension + Spring Config
@EnableAutoConfiguration
class TracingTestWithSBTest {

  @Autowired
  private InstrumentedComponent instrumentedComponent;

  @Spans
  private SpanCollector spanCollector;

  @Test
  void smoke() {

    this.instrumentedComponent.doSomethingWithTrace();

    TracingAssertions.assertThat(this.spanCollector.getFinishedSpans())
        .hasNumberOfSpansEqualTo(1)
        .hasASpanWithName("instrumented-component-span");

  }

  @Test
  void assertTags() {

    this.instrumentedComponent.doSomethingWithTrace();

    TracingAssertions.assertThat(this.spanCollector.getFinishedSpans())
        .hasNumberOfSpansEqualTo(1)
        .assertThatASpanWithNameEqualTo("instrumented-component-span")
        .hasTag("tag", "tag-value");
  }
}

Where the key points would be:

• The annotation @TracingTest would declare the tracing beans to be used by Spring Boot auto-configurations
• The annotation @TracingTest would contain a junit extension to manage the tests lifecycle.
• The user test would not be coupled to any vendor, just to micrometer-tracing api. The SpanColletor is a generic class to decouple the tests from the vendor classes.
• The TracingAsserts would be done using the micrometer-api

I have a naive approach with the opentelemetry vendor. If you feel that it could be useful, I could share it with you, and if you like it, contribute to the project.