proposal: testing: Support external packages to call testing.MainStart

[emcfarlane]

Systems simulating go test have two methods to invoke tests:

• testing.Main https://pkg.go.dev/testing#Main
• testing.MainStart https://pkg.go.dev/testing#MainStart

From the doc comments for Main, MainStart is preferred:

Systems simulating "go test" should be updated to use MainStart.

Previously, before go1.18, the internal interface testDeps could be satisfied by an external package. Upgrading to go1.18 the new internal interface contains methods with references to a private struct corpusEntry for the added fuzzing support. MainStart isn't part of the go compatibility promise. I propose providing an implementation of testDeps like

go/src/testing/testing.go

Line 1569 in 0ed31eb

type matchStringOnly func(pat, str string) (bool, error)

that could be used by external packages to call MainStart.

[seankhliao]

cc @bcmills

[emcfarlane]

My mistake, struct isn't private but an alias:

go/src/internal/fuzz/fuzz.go

Line 459 in f985833

type CorpusEntry = struct {

Would be nice to have a defined public testdeps implementation but not a blocker, happy to close.

[ianlancetaylor]

Doesn't seem like there is anything we need to do here, so closing. Please comment if you disagree.