Fix HTTP challenge router unexpected delayed creation

pkg/provider/aggregator/aggregator_test.go

@@ -0,0 +1,79 @@
+package aggregator
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v2/pkg/config/dynamic"
+	"github.com/traefik/traefik/v2/pkg/provider"
+	"github.com/traefik/traefik/v2/pkg/safe"
+)
+
+func TestProviderAggregator_Provide(t *testing.T) {
+	aggregator := ProviderAggregator{
+		internalProvider: &providerMock{"internal"},
+		fileProvider:     &providerMock{"file"},
+		providers: []provider.Provider{
+			&providerMock{"salad"},
+			&providerMock{"tomato"},
+			&providerMock{"onion"},
+		},
+	}
+
+	cfgCh := make(chan dynamic.Message)
+	errCh := make(chan error)
+	pool := safe.NewPool(context.Background())
+
+	t.Cleanup(pool.Stop)
+
+	go func() {
+		errCh <- aggregator.Provide(cfgCh, pool)
+	}()
+
+	// Make sure the file provider is always called first, followed by the internal provider.
+	requireReceivedMessageFromProviders(t, cfgCh, []string{"file"})
+	requireReceivedMessageFromProviders(t, cfgCh, []string{"internal"})
+
+	// Check if all providers have been called, the order doesn't matter.
+	requireReceivedMessageFromProviders(t, cfgCh, []string{"salad", "tomato", "onion"})
+
+	require.NoError(t, <-errCh)
+}
+
+// requireReceivedMessageFromProviders makes sure the given providers have emitted a message on the given message channel.
+// Providers order is not enforced.
+func requireReceivedMessageFromProviders(t *testing.T, cfgCh <-chan dynamic.Message, names []string) {
+	t.Helper()
+
+	var msg dynamic.Message
+	var receivedMessagesFrom []string
+
+	for range names {
+		select {
+		case <-time.After(10 * time.Millisecond):
+		case msg = <-cfgCh:
+			receivedMessagesFrom = append(receivedMessagesFrom, msg.ProviderName)
+		}
+	}
+
+	require.ElementsMatch(t, names, receivedMessagesFrom)
+}
+
+type providerMock struct {
+	Name string
+}
+
+func (p *providerMock) Init() error {
+	return nil
+}
+
+func (p *providerMock) Provide(configurationChan chan<- dynamic.Message, pool *safe.Pool) error {
+	configurationChan <- dynamic.Message{
+		ProviderName:  p.Name,
+		Configuration: &dynamic.Configuration{},
+	}
+
+	return nil
+}