feat(notify): Add NewWithServices() constructor function

AddNewWithServices() accepts a variadic list of services and returns a
new, by New() created, Notify instance with the list of services set as
its notifiers.

If no services are given it's the functionally identical to just calling
New().

Calling NewWithServices() with a list of services is functionally equal
to calling New() and then UseServices().

notify.go

@@ -66,6 +66,15 @@ func New() *Notify {
 	return NewWithOptions()
 }
 
+// NewWithServices returns a new instance of Notify with the given services. By default, the Notify instance is enabled.
+// If no services are provided, it returns a new Notify instance with default options.
+func NewWithServices(services ...Notifier) *Notify {
+	n := New()
+	n.UseServices(services...)
+
+	return n
+}
+
 // Create the package level Notify instance.
 var std = New()
 

notify_test.go

@@ -4,6 +4,8 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+
+	"github.com/nikoksr/notify/service/mail"
 )
 
 func TestNew(t *testing.T) {
@@ -64,3 +66,34 @@ func TestDefault(t *testing.T) {
 		t.Error("Default() did not return the default Notifier")
 	}
 }
+
+func TestNewWithServices(t *testing.T) {
+	t.Parallel()
+
+	n1 := NewWithServices()
+	if n1 == nil {
+		t.Fatal("NewWithServices() returned nil")
+	}
+
+	n2 := NewWithServices(nil)
+	if n2 == nil {
+		t.Fatal("NewWithServices(nil) returned nil")
+	}
+	if len(n2.notifiers) != 0 {
+		t.Error("NewWithServices(nil) did not return empty Notifier")
+	}
+
+	mailService := mail.New("", "")
+	n3 := NewWithServices(mailService)
+	if n3 == nil {
+		t.Fatal("NewWithServices(mail.New()) returned nil")
+	}
+	if len(n3.notifiers) != 1 {
+		t.Errorf("NewWithServices(mail.New()) was expected to have 1 notifier but had %d", len(n3.notifiers))
+	} else {
+		diff := cmp.Diff(n3.notifiers[0], mailService, cmp.AllowUnexported(mail.Mail{}))
+		if diff != "" {
+			t.Errorf("NewWithServices(mail.New()) did not correctly use service:\n%s", diff)
+		}
+	}
+}