2 posts tagged with "Testing"

Application Insights bugs tend to fall into one of two categories. Either the SDK sends something and you never see it in the portal - wrong connection string, wrong environment variable, telemetry initializer stripping the data - or it sends something you did not intend, and you only find out a week later when billing shows an unexpected spike. Both categories share one root cause: there is no fast, local feedback loop.

The standard debugging advice is to enable DiagnosticsTelemetryModule, or to tail the Fiddler capture, or to deploy to a dev environment and wait for the portal to ingest the data. All of those paths are slow. Some require a cloud subscription you might not have access to from the machine you are debugging on.

Topaz emulates the Application Insights ingestion API (/v2/track) and the query API (/v1/apps/{ikey}/query) locally. The SDK points at localhost, sends telemetry as it normally would, and you can query the ingested data immediately - from code, from the Topaz Portal, or from a KQL query in your terminal.

There is a certain category of test that feels good to write but does not actually test what you think it does. Retry logic sits squarely in that category.

The usual pattern is this: inject a fake HttpMessageHandler, make it return a 429 or 503 on the first N calls, assert that the code retried and eventually succeeded. The test passes. You ship with confidence. Then, in production, a real throttling event triggers a path through the Azure SDK that your mock never covered, and the retry policy does not behave the way the test implied.

The issue is not that the mock is wrong. It is that the mock bypasses the entire SDK transport layer. When you return a 429 from a fake handler, you are testing whether your own retry wrapper handles it correctly. You are not testing whether Azure.Core's built-in retry pipeline fires, whether the Retry-After header is respected, or whether the SDK's own exception hierarchy propagates through your application code the way you assumed. That is a different bar entirely.