Add more tests for RemoveRange

We were lacking sufficient coverage for the overload that takes an ImmutableArray<T>.  This essentially duplicates the RemoveRangeEnumerableTest but with an ImmutableArray<T> instead of IEnumerable<T> argument.

Author: stephentoub

src/System.Collections.Immutable/tests/ImmutableArrayTest.cs

@@ -826,6 +826,8 @@ public void RemoveRange()
         {
             Assert.Throws<ArgumentOutOfRangeException>(() => s_empty.RemoveRange(0, 0));
             Assert.Throws<NullReferenceException>(() => s_emptyDefault.RemoveRange(0, 0));
+            Assert.Throws<ArgumentOutOfRangeException>(() => s_emptyDefault.RemoveRange(-1, 0));
+            Assert.Throws<NullReferenceException>(() => s_emptyDefault.RemoveRange(0, -1));
             Assert.Throws<ArgumentOutOfRangeException>(() => s_oneElement.RemoveRange(1, 0));
             Assert.Throws<ArgumentOutOfRangeException>(() => s_empty.RemoveRange(-1, 0));
             Assert.Throws<ArgumentOutOfRangeException>(() => s_oneElement.RemoveRange(0, 2));
@@ -913,6 +915,35 @@ public void RemoveRangeEnumerableTest()
             Assert.Equal(new[] { 1, 3 }, listWithDuplicates.RemoveRange(new[] { 2, 2, 2 }));
         }
 
+        [Fact]
+        public void RemoveRangeImmutableArrayTest()
+        {
+            var list = ImmutableArray.Create(1, 2, 3);
+
+            ImmutableArray<int> removed2 = list.RemoveRange(ImmutableArray.Create(2));
+            Assert.Equal(2, removed2.Length);
+            Assert.Equal(new[] { 1, 3 }, removed2);
+
+            ImmutableArray<int> removed13 = list.RemoveRange(ImmutableArray.Create(1, 3, 5));
+            Assert.Equal(1, removed13.Length);
+            Assert.Equal(new[] { 2 }, removed13);
+
+            Assert.Equal(new[] { 1, 3, 6, 8, 9 }, ImmutableArray.CreateRange(Enumerable.Range(1, 10)).RemoveRange(ImmutableArray.Create(2, 4, 5, 7, 10)));
+            Assert.Equal(new[] { 3, 6, 8, 9 }, ImmutableArray.CreateRange(Enumerable.Range(1, 10)).RemoveRange(ImmutableArray.Create(1, 2, 4, 5, 7, 10)));
+
+            Assert.Equal(list, list.RemoveRange(ImmutableArray.Create(5)));
+            Assert.Equal(ImmutableArray.Create<int>(), ImmutableArray.Create<int>().RemoveRange(ImmutableArray.Create(1)));
+
+            var listWithDuplicates = ImmutableArray.Create(1, 2, 2, 3);
+            Assert.Equal(new[] { 1, 2, 3 }, listWithDuplicates.RemoveRange(ImmutableArray.Create(2)));
+            Assert.Equal(new[] { 1, 3 }, listWithDuplicates.RemoveRange(ImmutableArray.Create(2, 2)));
+            Assert.Equal(new[] { 1, 3 }, listWithDuplicates.RemoveRange(ImmutableArray.Create(2, 2, 2)));
+
+            Assert.Equal(new[] { 2, 3 }, list.RemoveRange(ImmutableArray.Create(42), EverythingEqual<int>.Default));
+            Assert.Equal(new[] { 3 }, list.RemoveRange(ImmutableArray.Create(42, 42), EverythingEqual<int>.Default));
+            Assert.Equal(new int[0], list.RemoveRange(ImmutableArray.Create(42, 42, 42), EverythingEqual<int>.Default));
+        }
+
         [Fact]
         public void Replace()
         {