An error filter example

error_filter_test.go

package foo_test

import (
	"context"
	"errors"
	"reflect"
	"testing"
	"time"

	. "github.com/onsi/ginkgo/v2"
	. "github.com/onsi/gomega"
)

func TestFoo(t *testing.T) {
	RegisterFailHandler(Fail)
	RunSpecs(t, "Foo Suite")
}

var NotFoundErr = errors.New("not found")

var errInterface = reflect.TypeOf((*error)(nil)).Elem()

func ErrorFilter(in any) any {
	inType := reflect.TypeOf(in)
	inValue := reflect.ValueOf(in)
	return reflect.MakeFunc(inType, func(args []reflect.Value) []reflect.Value {
		out := inValue.Call(args)
		if len(out) > 0 {
			lastValue := out[len(out)-1]
			last := lastValue.Interface()
			if last != nil && lastValue.Type().Implements(errInterface) && errors.Is(last.(error), NotFoundErr) {
				out[len(out)-1] = reflect.Zero(errInterface)
			}
		}
		return out
	}).Interface()
}

func myFunc(ctx context.Context, name string) error {
	if name == "not-found" {
		return NotFoundErr
	} else if name == "no-error" {
		return nil
	} else if name == "timeout" {
		<-ctx.Done()
	}
	return errors.New("boom")
}

var _ = Describe("cases", func() {
	It("passes", func() {
		DeferCleanup(ErrorFilter(myFunc), "no-error")
	})
	It("times out", func() {
		DeferCleanup(ErrorFilter(myFunc), "timeout", NodeTimeout(time.Millisecond*100))
	})
	It("pases because of the filter", func() {
		DeferCleanup(ErrorFilter(myFunc), "not-found")
	})
	It("fails", func() {
		DeferCleanup(ErrorFilter(myFunc), "boom")
	})
})