Added integration test for new method on IContentService.

Author: AndyButland

tests/Umbraco.Tests.Integration/Umbraco.Core/Services/ContentServiceTests.cs

@@ -687,6 +687,25 @@ public void Can_Get_Content_For_Expiration()
         Assert.That(contents.Count(), Is.EqualTo(1));
     }
 
+    [Test]
+    public void Can_Get_Scheduled_Content_Keys()
+    {
+        // Arrange
+        var root = ContentService.GetById(Textpage.Id);
+        ContentService.Publish(root!, root!.AvailableCultures.ToArray());
+        var content = ContentService.GetById(Subpage.Id);
+        var contentSchedule = ContentScheduleCollection.CreateWithEntry(DateTime.UtcNow.AddDays(1), null);
+        ContentService.PersistContentSchedule(content!, contentSchedule);
+        ContentService.Publish(content, content.AvailableCultures.ToArray());
+
+        // Act
+        var keys = ContentService.GetScheduledContentKeys([Textpage.Key, Subpage.Key, Subpage2.Key]).ToList();
+
+        // Assert
+        Assert.AreEqual(1, keys.Count);
+        Assert.AreEqual(Subpage.Key, keys.First());
+    }
+
     [Test]
     public void Can_Get_Content_For_Release()
     {