mtest.go

// Package mtest is a support library for writing tests.
package mtest

// TB is the subset of the testing.TB interface used by this package.
type TB interface {
	Cleanup(func())
	Fatalf(string, ...any)
	Helper()
}

// MustPanic executes a function f that is expected to panic.
// If it does so, MustPanic returns the value recovered from the
// panic. Otherwise, it logs a fatal error in t.
func MustPanic(t TB, f func()) (val any) {
	t.Helper()
	defer func() { val = recover() }()
	f()
	t.Fatalf("expected panic was not observed")
	return
}

// MustPanicf executes a function f that is expected to panic.  If it does so,
// MustPanicf returns the value recovered from the panic. Otherwise it logs a
// fatal error in t.
func MustPanicf(t TB, f func(), msg string, args ...any) (val any) {
	t.Helper()
	defer func() { val = recover() }()
	f()
	t.Fatalf(msg, args...)
	return
}

// Swap replaces the target of p with v, and restores the original value when
// the governing test exits. It returns the original value.
func Swap[T any](t TB, p *T, v T) T {
	save := *p
	*p = v
	t.Cleanup(func() { *p = save })
	return save
}