go/src/cmd/internal/script/scripttest/setup.go

// SetupTestGoRoot sets up a temporary GOROOT for use with script test
// execution. It copies the existing goroot bin and pkg dirs using
// symlinks (if possible) or raw copying. Return value is the path to
// the newly created testgoroot dir.
func SetupTestGoRoot(t *testing.T, tmpdir string, goroot string) string { … }

// ReplaceGoToolInTestGoRoot replaces the go tool binary toolname with
// an alternate executable newtoolpath within a test GOROOT directory
// previously created by SetupTestGoRoot.
func ReplaceGoToolInTestGoRoot(t *testing.T, testgoroot, toolname, newtoolpath string) { … }

// linkOrCopy creates a link to src at dst, or if the symlink fails
// (platform doesn't support) then copies src to dst.
func linkOrCopy(t *testing.T, src, dst string) { … }