Port #2463 to v2

bradwilson · bradwilson · commit 19618efd329b · 2022-01-18T08:59:33.000-08:00
diff --git a/src/xunit.assert/Asserts b/src/xunit.assert/Asserts
@@ -1 +1 @@
-Subproject commit 08ea727abe286ecc3bf340959d909cba7b9b195e
+Subproject commit 43e3e208a597bc1a4c77f2665f39f98e7401c157
diff --git a/test/test.xunit.assert/Asserts/CollectionAssertsTests.cs b/test/test.xunit.assert/Asserts/CollectionAssertsTests.cs
@@ -925,6 +925,14 @@ public static void Equivalence()
 
 			Assert.Equal(expected, actual);
 		}
+
+		[Fact]
+		public static void EnumeratesOnlyOnce()
+		{
+			var expected = new[] { 1, 2, 3, 4, 5 };
+			var actual = new RunOnceEnumerable<int>(expected);
+			Assert.Equal(expected, actual);
+		}
 	}
 
 	public class EqualDictionary
@@ -1350,6 +1358,26 @@ public static void PredicateTooManyMatches()
 		}
 	}
 
+	sealed class RunOnceEnumerable<T> : IEnumerable<T>
+	{
+		private readonly IEnumerable<T> _source;
+		private bool _called;
+
+		public RunOnceEnumerable(IEnumerable<T> source)
+		{
+			_source = source;
+		}
+
+		public IEnumerator<T> GetEnumerator()
+		{
+			Assert.False(_called, "GetEnumerator() was called more than once");
+			_called = true;
+			return _source.GetEnumerator();
+		}
+
+		IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+	}
+
 	sealed class SpyEnumerator<T> : IEnumerable<T>, IEnumerator<T>
 	{
 		IEnumerator<T>? innerEnumerator;
