Add observable collection tests

UnitTests/MvvmCross.UnitTest/ViewModels/MvxObservableCollectionTest.cs

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+using System;
+using System.Collections.Specialized;
+using MvvmCross.Base;
+using MvvmCross.Test;
+using MvvmCross.ViewModels;
+using Xunit;
+
+namespace MvvmCross.UnitTest.ViewModels
+{
+    [Collection("MvxTest")]
+    public class MvxObservableCollectionTest
+    {
+        MvxTestFixture _fixture;
+
+        public MvxObservableCollectionTest(MvxTestFixture fixture)
+        {
+            _fixture = fixture;
+            _fixture.Ioc.RegisterSingleton<IMvxMainThreadDispatcher>(new DummyDispatcher());
+        }
+
+        public class DummyDispatcher : MvxSingleton<IMvxMainThreadDispatcher>, IMvxMainThreadDispatcher
+        {
+            public bool RequestMainThreadAction(Action action, bool maskExceptions = true)
+            {
+                action?.Invoke();
+                return true;
+            }
+        }
+
+        [Fact]
+        public void AddRangeSuppressesChangesTest()
+        {
+            var collection = new MvxObservableCollection<string>();
+            var invokeCount = 0;
+            collection.CollectionChanged += (s, e) =>
+            {
+                invokeCount++;
+            };
+
+            collection.Add("Foo");
+
+            Assert.Equal(1, invokeCount);
+            Assert.Contains("Foo", collection);
+
+            var newItems = new[] { "Bar", "Baz", "Herp", "Derp" };
+            collection.AddRange(newItems);
+
+            Assert.Equal(2, invokeCount);
+
+            foreach (var item in newItems)
+                Assert.Contains(item, collection);
+        }
+
+        [Fact]
+        public void AddRangeIsAddActionTest()
+        {
+            var collection = new MvxObservableCollection<string>();
+            collection.CollectionChanged += (s, e) => {
+                Assert.Equal(NotifyCollectionChangedAction.Add, e.Action);
+            };
+            collection.AddRange(new[] { "Bar", "Baz", "Herp", "Derp" });
+        }
+
+        [Fact]
+        public void ValidateStartingIndexOnAddRangeTest()
+        {
+            var collection = new MvxObservableCollection<string>();
+            var newItems = new[] { "Bar", "Baz", "Herp", "Derp" };
+
+            NotifyCollectionChangedEventHandler handler = (s, a) =>
+            {
+                Assert.Equal(0, a.NewStartingIndex);
+                Assert.Equal(newItems.Length, a.NewItems.Count);
+                Assert.Null(a.OldItems);
+            };
+
+            collection.CollectionChanged += handler;
+
+            collection.AddRange(newItems);
+            var newStartIndex = collection.Count;
+
+            collection.CollectionChanged -= handler;
+
+            handler = (s, a) => {
+                Assert.Equal(newStartIndex, a.NewStartingIndex);
+                Assert.Equal(newItems.Length, a.NewItems.Count);
+            };
+
+            collection.CollectionChanged += handler;
+
+            collection.AddRange(newItems);
+        }
+
+        [Fact]
+        public void AddRangeThrowsArgumentNullExceptionOnNullInput()
+        {
+            var collection = new MvxObservableCollection<string>();
+            Assert.Throws<ArgumentNullException>(() => collection.AddRange(null));
+        }
+    }
+}