proposal: testing: optional prefix for error output #68613

Proposal Details

Proposal

I propose the addition of a go test flag that will add a prefix to the output of t.Error(f) and t.Fatal(f). For example, go test -errlogprefix "Error: " would cause t.Error("it failed") to output Error: it failed.

Alternatively a flag that specifies a template for error message printing would be even more useful, something like -errlogformat "Error: {{.Message}}". Beyond the basic Message field, the context could include additional info such as the location.

Motivation

When the user executes a Go test in vscode (with vscode-go), I want to tell the user what caused the error to fail. vscode provides a mechanism for this - when I report the failure of the test, I can provide messages associated with that failure. However, I have no way of knowing which messages should be associated with the failure. However if this proposal is accepted, I could specify some sequence of bytes as the prefix, and detect that sequence of bytes when processing test output.