Added test for ByteString.CopyFrom(ReadOnlySpan<byte> bytes)

csharp/src/Google.Protobuf.Test/ByteStringTest.cs

@@ -110,6 +110,18 @@ namespace Google.Protobuf
             Assert.AreEqual(10, bs[0]);
         }
 
+        [Test]
+        public void CopyFromReadOnlySpanCopiesContents()
+        {
+            byte[] data = new byte[1];
+            data[0] = 10;
+            ReadOnlySpan<byte> byteSpan = data;
+            var bs = ByteString.CopyFrom(byteSpan);
+            Assert.AreEqual(10, bs[0]);
+            data[0] = 5;
+            Assert.AreEqual(10, bs[0]);
+        }
+
         [Test]
         public void ToByteArrayCopiesContents()
         {
@@ -249,5 +261,6 @@ namespace Google.Protobuf
             var copied = byteString.Memory.ToArray();
             CollectionAssert.AreEqual(byteString, copied);
         }
+
     }
 }