Fix go vet errors

Unfortunatelly the errgroup.Group is not copyable so
had to handle implicity initialization in all methods.

internal/errgroup/errgroup.go

@@ -16,20 +16,23 @@ import (
 // The Group is superior errgroup.Group which aborts whole group
 // execution when parent context is cancelled
 type Group struct {
-	grp errgroup.Group
+	grp *errgroup.Group
 	ctx context.Context
 }
 
 // WithContext creates Group and store inside parent context
 // so the Go method would respect parent context cancellation
 func WithContext(ctx context.Context) (*Group, context.Context) {
 	grp, child_ctx := errgroup.WithContext(ctx)
-	return &Group{grp: *grp, ctx: ctx}, child_ctx
+	return &Group{grp: grp, ctx: ctx}, child_ctx
 }
 
 // Go runs the provided f function in a dedicated goroutine and waits for its
 // completion or for the parent context cancellation.
 func (g *Group) Go(f func() error) {
+	if g.grp == nil {
+		g.grp = &errgroup.Group{}
+	}
 	g.grp.Go(g.wrap(f))
 }
 
@@ -38,6 +41,9 @@ func (g *Group) Go(f func() error) {
 // If the error group was created via WithContext then the Wait returns error
 // of cancelled parent context prior any functions calls complete.
 func (g *Group) Wait() error {
+	if g.grp == nil {
+		g.grp = &errgroup.Group{}
+	}
 	return g.grp.Wait()
 }
 
@@ -49,6 +55,9 @@ func (g *Group) Wait() error {
 //
 // The limit must not be modified while any goroutines in the group are active.
 func (g *Group) SetLimit(n int) {
+	if g.grp == nil {
+		g.grp = &errgroup.Group{}
+	}
 	g.grp.SetLimit(n)
 }
 
@@ -57,6 +66,9 @@ func (g *Group) SetLimit(n int) {
 //
 // The return value reports whether the goroutine was started.
 func (g *Group) TryGo(f func() error) bool {
+	if g.grp == nil {
+		g.grp = &errgroup.Group{}
+	}
 	return g.grp.TryGo(g.wrap(f))
 }
 

rep_test.go

@@ -134,6 +134,7 @@ func TestCancellation(t *testing.T) {
 
 		defer wg.Done()
 		repCtx, cancel := context.WithCancel(context.Background())
+		defer cancel()
 		rep := zmq4.NewRep(repCtx)
 		defer rep.Close()