add syntax sugar to run function on non ok sandbox results

sandbox/Run.go

@@ -50,6 +50,17 @@ func (ro RunOutcome) Trace() string {
 	return buf.String()
 }
 
+// OnNotOK will execute the argument block when the OK state is false.
+func (ro RunOutcome) OnNotOK(blk func()) {
+	if ro.OK {
+		return
+	}
+	if blk == nil {
+		return
+	}
+	blk()
+}
+
 func stackHasGoexit() bool {
 	const goexitFuncName = "runtime.Goexit"
 	return caller.Until(func(frame runtime.Frame) bool {

sandbox/Run_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"go.llib.dev/testcase"
+	"go.llib.dev/testcase/assert"
 	"go.llib.dev/testcase/sandbox"
 )
 
@@ -72,3 +73,22 @@ func TestRun(t *testing.T) {
 		})
 	})
 }
+
+func TestRunOutcome_OnNotOK(t *testing.T) {
+	t.Run("happy", func(t *testing.T) {
+		var ran bool
+		sandbox.Run(func() {}).
+			OnNotOK(func() { ran = true })
+		assert.False(t, ran)
+	})
+	t.Run("rainy", func(t *testing.T) {
+		var ran bool
+		sandbox.Run(func() { panic("boom") }).
+			OnNotOK(func() { ran = true })
+		assert.True(t, ran)
+	})
+	t.Run("rainy plus nil block", func(t *testing.T) {
+		sandbox.Run(func() { panic("boom") }).
+			OnNotOK(nil)
+	})
+}