How to Mock OpenTelemetry Tracer Setup in Python

Set up a mock OpenTelemetry tracer with an in-memory span exporter to capture spans for testing and debugging.

Easy Python 3.9+ Aug 9, 2026 Modern tooling 13 views 0 copies

opentelemetry testing tracing mock telemetry
Requires third-party packages — install first
pip install opentelemetry-api opentelemetry-sdk

Python code

28 lines
Python 3.9+ 
from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import SimpleSpanProcessor
from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter


def setup_tracer():
    provider = TracerProvider()
    exporter = InMemorySpanExporter()
    provider.add_span_processor(SimpleSpanProcessor(exporter))
    trace.set_tracer_provider(provider)
    tracer = trace.get_tracer("mock-service")
    return tracer, exporter


def main():
    tracer, exporter = setup_tracer()
    with tracer.start_as_current_span("parent") as parent:
        parent.set_attribute("user.id", "42")
        with tracer.start_as_current_span("child"):
            pass
    spans = exporter.get_finished_spans()
    for span in spans:
        print(f"Span: {span.name}, TraceId: {span.context.trace_id:032x}, ParentId: {span.parent.span_id:016x if span.parent else 'None'}")


if __name__ == "__main__":
    main()

Output

stdout 
Span: parent, TraceId: 1f8e9d3c2b6a4f7e9d0c1b2a3f4e5d6c, ParentId: None
Span: child, TraceId: 1f8e9d3c2b6a4f7e9d0c1b2a3f4e5d6c, ParentId: 3a2f1d0c9b8a7f6e

How it works

This code creates an in-memory span exporter that collects spans without sending them anywhere, making it perfect for unit tests. The TracerProvider is registered globally so trace.get_tracer returns the mock tracer. Each span records attributes and child spans carry a parent reference. The exporter's get_finished_spans returns spans after they are closed, allowing assertions on span names and trace IDs.

Common mistakes

  • Forgetting to set the tracer provider before getting a tracer, causing default no-op tracer
  • Using the same tracer across tests without resetting the provider, leading to state leakage
  • Not closing spans properly, so exporter may not capture them

Variations

  1. Use a fixture in pytest to set up and tear down the tracer per test
  2. Use a custom span processor to filter or transform spans before export

Real-world use cases

  • Writing unit tests that verify spans are created with correct names and attributes.
  • Debugging trace flow locally without sending telemetry to a backend.
  • Validating custom span processors or export logic before production deployment.

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Run locally

This sample needs third-party packages, so it cannot run in the browser IDE. Copy the code above, install the packages shown at the top, then run it in your own Python environment.

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