Test null check in Timestamps.TryParse and document parameters (#285)

Signed-off-by: Safia Abdalla <[email protected]>

src/CloudNative.CloudEvents/Timestamps.cs

@@ -44,12 +44,11 @@ internal static class Timestamps
         /// <summary>
         /// Attempts to parse a string as an RFC-3339-formatted date/time and UTC offset.
         /// </summary>
-        /// <param name="input"></param>
-        /// <param name="result"></param>
-        /// <returns></returns>
-        public static bool TryParse(string input, out DateTimeOffset result)
+        /// <param name="input">A string to be parsed as a <see cref="DateTimeOffset"/>.</param>
+        /// <param name="result">A <see cref="DateTimeOffset"/> parsed from the <paramref name="input"/>.</param>
+        /// <returns><see langword="true"/> if <paramref name="input"/> was parsed successfully, <see langword="false"/> otherwise.</returns>
+        internal static bool TryParse(string input, out DateTimeOffset result)
         {
-            // TODO: Check this and add a test
             Validation.CheckNotNull(input, nameof(input));
 
             if (input.Length < MinLength) // "yyyy-MM-ddTHH:mm:ssZ" is the shortest possible value.

test/CloudNative.CloudEvents.UnitTests/TimestampsTest.cs

@@ -1,4 +1,4 @@
-// Copyright 2021 Cloud Native Foundation. 
+// Copyright 2021 Cloud Native Foundation.
 // Licensed under the Apache 2.0 license.
 // See LICENSE file in the project root for full license information.
 
@@ -123,6 +123,13 @@ public void Parse_Failure(string text)
             Assert.Throws<FormatException>(() => Timestamps.Parse(text));
         }
 
+        [Fact]
+        public void Parse_Null()
+        {
+            Assert.Throws<ArgumentNullException>(() => Timestamps.TryParse(null!, out _));
+            Assert.Throws<ArgumentNullException>(() => Timestamps.Parse(null!));
+        }
+
         /// <summary>
         /// As we're already testing parsing thoroughly, the simplest way of providing
         /// a value to format is to parse a string. Many examples will round-trip, in which