Go test events

Running tests with the -json flag or passing test output through go tool test2json1 will produce a stream of JSON events. Each event specifies an action, such as run, pass, output, etc. An event may specify what test it belongs to. The VSCode Go test controller must capture these events in order to notify VSCode of test output and lifecycle events.


Processing test events generated by TestXxx(*testing.T) functions is easy. Events with an empty Test field can be ignored, and all other events have a meaningful Action field. Output is recorded, and run/pass/fail/skip events are converted to VSCode test API events.

go#37555 did require special handling, but that only appeared in Go 1.14 and was backported to 1.14.1.


Test events generated by BenchmarkXxx(*testing.B) functions require significantly more processing. If a benchmark fails or is skipped, the Test and Action fields are populated appropriately. Otherwise, Test is empty and Action is always output. Thus, nominal lifecycle events (run/pass) must be deduced purely from test output. When a benchmark begins, an output such as BenchmarkFooBar\n is produced. When a benchmark completes, an output such as BencmarkFooBar-4 123456 123.4 ns/op 123 B/op 12 allocs/op is produced. No explicit run or pass events are generated. Thus:

  • When BenchmarkFooBar\n is seen, the benchmark will be marked as running
  • When an explicit fail/skip is seen, the benchmark will be marked as failed/skipped
  • When benchmark results are seen, the benchmark will be marked as passed

Thus, a benchmark that does not produce results (and does not fail or skip) will never produce an event indicating that it has completed. Benchmarks that call (*testing.B).Run will not produce results. In practice, this means that any incomplete benchmarks must be explicitly marked as passed once go test returns.