var fromToolchainTests = []testCase1[string, string]{
	{"go1.2.3", "1.2.3"},
	{"1.2.3", ""},
	{"go1.2.3+bigcorp", ""},
	{"go1.2.3-bigcorp", "1.2.3"},
	{"go1.2.3-bigcorp more text", "1.2.3"},
	{"gccgo-go1.23rc4", ""},
	{"gccgo-go1.23rc4-bigdwarf", ""},

cat go.mod
go list -f '{{.Module.GoVersion}}'
stdout 1.22

# Adding a@v1.0.01 should upgrade to Go 1.23rc1.
cp go.mod go.mod1
go get example.com/a@v1.0.1
stderr '^go: upgraded go 1.22 => 1.23rc1\ngo: upgraded example.com/a v1.0.0 => v1.0.1\ngo: upgraded example.com/b v1.0.0 => v1.0.1$'
go list -f '{{.Module.GoVersion}}'
stdout 1.23rc1

# Repeating the update with go@1.24.0 should use that Go version.
cp go.mod1 go.mod

}

// Prev returns the Go major release immediately preceding v,
// or v itself if v is the first Go major release (1.0) or not a supported
// Go version.
//
// Examples:
//
//	Prev("1.2") = "1.1"
//	Prev("1.3rc4") = "1.2"
func Prev(x string) string {
	v := gover.Parse(x)
	if gover.CmpInt(v.Minor, "1") <= 0 {
		return v.Major
	}
	return v.Major + "." + gover.DecInt(v.Minor)
}

	{"1.2", false},  // == 1.2.0
	{"1", false},    // == 1.0.0
}

func TestPrev(t *testing.T) { test1(t, prevTests, "Prev", Prev) }

var prevTests = []testCase1[string, string]{
	{"", ""},
	{"0", "0"},
	{"1.3rc4", "1.2"},
	{"1.3.5", "1.2"},
	{"1.3", "1.2"},
	{"1", "1"},
	{"1.99999999999999999", "1.99999999999999998"},
	{"1.40000000000000000", "1.39999999999999999"},
}