Add errgroup tests

By geClaude

Signed-off-by: Nelo-T. Wallus <red.brush9525@fastmail.com>
Signed-off-by: Nelo-T. Wallus <n.wallus@sap.com>

Author: ntnn

pkg/errgroup/errgroup_test.go

@@ -0,0 +1,392 @@
+/*
+Copyright 2025 The KCP Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package errgroup
+
+import (
+	"context"
+	"errors"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGroup_NoContext_NoRunners(t *testing.T) {
+	var g Group
+	err := g.Wait()
+	require.NoError(t, err)
+}
+
+func TestGroup_WithContext_NoRunners(t *testing.T) {
+	g := WithContext(context.Background())
+	require.NotNil(t, g)
+	err := g.Wait()
+	require.NoError(t, err)
+}
+
+func TestGroup_NoContext_NilRunner(t *testing.T) {
+	var g Group
+	g.Go(nil)
+	err := g.Wait()
+	require.NoError(t, err)
+}
+
+func TestGroup_WithContext_NilRunner(t *testing.T) {
+	g := WithContext(context.Background())
+	g.Go(nil)
+	err := g.Wait()
+	require.NoError(t, err)
+}
+
+func TestGroup_NoContext_SuccessfulRunners(t *testing.T) {
+	var g Group
+	var count atomic.Int32
+
+	for range 5 {
+		g.Go(func(_ context.Context) error {
+			count.Add(1)
+			return nil
+		})
+	}
+
+	err := g.Wait()
+	require.NoError(t, err)
+	assert.Equal(t, int32(5), count.Load())
+}
+
+func TestGroup_WithContext_SuccessfulRunners(t *testing.T) {
+	g := WithContext(context.Background())
+	var count atomic.Int32
+
+	for range 5 {
+		g.Go(func(_ context.Context) error {
+			count.Add(1)
+			return nil
+		})
+	}
+
+	err := g.Wait()
+	require.NoError(t, err)
+	assert.Equal(t, int32(5), count.Load())
+}
+
+func TestGroup_NoContext_SingleError(t *testing.T) {
+	var g Group
+	expected := errors.New("test error")
+
+	g.Go(func(_ context.Context) error {
+		return expected
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), expected.Error())
+}
+
+func TestGroup_WithContext_SingleError(t *testing.T) {
+	g := WithContext(context.Background())
+	expected := errors.New("test error")
+
+	g.Go(func(_ context.Context) error {
+		return expected
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), expected.Error())
+}
+
+func TestGroup_NoContext_MultipleErrors(t *testing.T) {
+	var g Group
+	err1 := errors.New("error one")
+	err2 := errors.New("error two")
+
+	g.Go(func(_ context.Context) error { return err1 })
+	g.Go(func(_ context.Context) error { return err2 })
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), err1.Error())
+	assert.Contains(t, err.Error(), err2.Error())
+}
+
+func TestGroup_WithContext_MultipleErrors(t *testing.T) {
+	g := WithContext(context.Background())
+	err1 := errors.New("error one")
+	err2 := errors.New("error two")
+
+	g.Go(func(_ context.Context) error { return err1 })
+	g.Go(func(_ context.Context) error { return err2 })
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), err1.Error())
+	assert.Contains(t, err.Error(), err2.Error())
+}
+
+func TestGroup_NoContext_MixedResults(t *testing.T) {
+	var g Group
+	expected := errors.New("some error")
+	var okCount atomic.Int32
+
+	g.Go(func(_ context.Context) error {
+		okCount.Add(1)
+		return nil
+	})
+	g.Go(func(_ context.Context) error {
+		return expected
+	})
+	g.Go(func(_ context.Context) error {
+		okCount.Add(1)
+		return nil
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), expected.Error())
+	assert.Equal(t, int32(2), okCount.Load())
+}
+
+func TestGroup_WithContext_MixedResults(t *testing.T) {
+	g := WithContext(context.Background())
+	expected := errors.New("some error")
+	var okCount atomic.Int32
+
+	g.Go(func(_ context.Context) error {
+		okCount.Add(1)
+		return nil
+	})
+	g.Go(func(_ context.Context) error {
+		return expected
+	})
+	g.Go(func(_ context.Context) error {
+		okCount.Add(1)
+		return nil
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), expected.Error())
+	assert.Equal(t, int32(2), okCount.Load())
+}
+
+func TestGroup_WithContext_ContextPassedToRunners(t *testing.T) {
+	type key struct{}
+	ctx := context.WithValue(context.Background(), key{}, "hello")
+	g := WithContext(ctx)
+
+	var got atomic.Value
+	g.Go(func(ctx context.Context) error {
+		got.Store(ctx.Value(key{}))
+		return nil
+	})
+
+	err := g.Wait()
+	require.NoError(t, err)
+	assert.Equal(t, "hello", got.Load())
+}
+
+func TestGroup_NoContext_RunnersGetBackgroundDerivedContext(t *testing.T) {
+	var g Group
+
+	var gotCtx atomic.Value
+	g.Go(func(ctx context.Context) error {
+		gotCtx.Store(ctx)
+		return nil
+	})
+
+	err := g.Wait()
+	require.NoError(t, err)
+	require.NotNil(t, gotCtx.Load())
+}
+
+func TestGroup_WithContext_CancelledParentContext(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // cancel immediately
+
+	g := WithContext(ctx)
+
+	var gotErr atomic.Value
+	g.Go(func(ctx context.Context) error {
+		<-ctx.Done()
+		gotErr.Store(ctx.Err())
+		return ctx.Err()
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.ErrorIs(t, gotErr.Load().(error), context.Canceled)
+}
+
+func TestGroup_NoContext_FailFast(t *testing.T) {
+	var g Group
+	g.FailFast = true
+
+	started := make(chan struct{})
+	g.Go(func(ctx context.Context) error {
+		close(started)
+		<-ctx.Done()
+		return ctx.Err()
+	})
+
+	// Ensure the first goroutine is running before triggering the error.
+	<-started
+
+	g.Go(func(_ context.Context) error {
+		return errors.New("fail")
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+}
+
+func TestGroup_WithContext_FailFast(t *testing.T) {
+	g := WithContext(context.Background())
+	g.FailFast = true
+
+	started := make(chan struct{})
+	g.Go(func(ctx context.Context) error {
+		close(started)
+		<-ctx.Done()
+		return ctx.Err()
+	})
+
+	// Ensure the first goroutine is running before triggering the error.
+	<-started
+
+	g.Go(func(_ context.Context) error {
+		return errors.New("fail")
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+}
+
+func TestGroup_WithContext_FailFastCancelsContext(t *testing.T) {
+	g := WithContext(context.Background())
+	g.FailFast = true
+
+	cancelled := make(chan struct{})
+	g.Go(func(ctx context.Context) error {
+		<-ctx.Done()
+		close(cancelled)
+		return nil
+	})
+
+	g.Go(func(_ context.Context) error {
+		return errors.New("trigger fail fast")
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+
+	// The cancelled channel should be closed because fail-fast
+	// cancels the context.
+	select {
+	case <-cancelled:
+		// expected
+	case <-time.After(time.Second):
+		t.Fatal("expected context to be cancelled by fail fast")
+	}
+}
+
+func TestGroup_NoContext_FailFastFalseDoesNotCancel(t *testing.T) {
+	var g Group
+	g.FailFast = false
+
+	var completed atomic.Bool
+	g.Go(func(ctx context.Context) error {
+		// Small sleep to ensure the error goroutine finishes first.
+		time.Sleep(50 * time.Millisecond)
+		completed.Store(true)
+		return nil
+	})
+
+	g.Go(func(_ context.Context) error {
+		return errors.New("error")
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.True(t, completed.Load(), "goroutine should complete even after another errors")
+}
+
+func TestGroup_WithContext_FailFastFalseDoesNotCancel(t *testing.T) {
+	g := WithContext(context.Background())
+	g.FailFast = false
+
+	var completed atomic.Bool
+	g.Go(func(ctx context.Context) error {
+		// Small sleep to ensure the error goroutine finishes first.
+		time.Sleep(50 * time.Millisecond)
+		completed.Store(true)
+		return nil
+	})
+
+	g.Go(func(_ context.Context) error {
+		return errors.New("error")
+	})
+
+	err := g.Wait()
+	require.Error(t, err)
+	assert.True(t, completed.Load(), "goroutine should complete even after another errors")
+}
+
+func TestGroup_WaitCalledMultipleTimes(t *testing.T) {
+	var g Group
+	g.Go(func(_ context.Context) error {
+		return errors.New("err")
+	})
+
+	err1 := g.Wait()
+	err2 := g.Wait()
+	require.Error(t, err1)
+	assert.Equal(t, err1.Error(), err2.Error(), "wait should return the same error on repeated calls")
+}
+
+func TestGroup_NilGroup_Wait(t *testing.T) {
+	// A zero-value Group should work without explicit initialization.
+	g := &Group{}
+	err := g.Wait()
+	require.NoError(t, err)
+}
+
+func TestGroup_NilGroup_GoNil(t *testing.T) {
+	g := &Group{}
+	g.Go(nil)
+	err := g.Wait()
+	require.NoError(t, err)
+}
+
+func TestGroup_WithContext_WaitCancelsContext(t *testing.T) {
+	ctx := context.Background()
+	g := WithContext(ctx)
+
+	var runnerCtx atomic.Value
+	g.Go(func(ctx context.Context) error {
+		runnerCtx.Store(ctx)
+		return nil
+	})
+
+	err := g.Wait()
+	require.NoError(t, err)
+
+	storedCtx := runnerCtx.Load().(context.Context)
+	assert.Error(t, storedCtx.Err(), "context should be cancelled after Wait returns")
+}