Added fallback format when no formating is specified for the Essentia…

…lsDate.ToString and EssentialsTime.ToString methods

Normally when an object is used in string interpolation, the object's parameterless ToString method is called for getting a string representation fo the object. But if the object implements the IFormattable interface - as both EssentialsDate and EssentialsTime do now - the ToString(string? format, IFormatProvider? provider) method will be called instead, but with the "format" parameter being null. In order to not introduce any breaking changes, the EssentialsDate.ToString(string? format, IFormatProvider? provider) and EssentialsTime.ToString(string? format, IFormatProvider? provider) methods have now been updated to return the same value as the parameterless EssentialsDate.ToString() and EssentialsTime.ToString() methods, which are an ISO 8601 formatted date and timestamp respectively.

src/Skybrud.Essentials/Time/EssentialsDate.cs

@@ -439,7 +439,7 @@ public string ToString([StringSyntax(StringSyntaxAttribute.DateTimeFormat)] stri
         /// <param name="provider">An object that supplies culture-specific formatting information.</param>
         /// <returns>A string representation of value of the current <see cref="EssentialsDate"/> object as specified by <paramref name="format"/> and <paramref name="provider"/>.</returns>
         public string ToString([StringSyntax(StringSyntaxAttribute.DateTimeFormat)] string? format, IFormatProvider? provider) {
-            return _dateTime.ToString(format, provider);
+            return _dateTime.ToString(string.IsNullOrWhiteSpace(format) ? "yyyy-MM-dd" : format, provider);
         }
 
         #endregion

src/Skybrud.Essentials/Time/EssentialsTime.cs

@@ -791,7 +791,7 @@ public string ToString([StringSyntax(StringSyntaxAttribute.DateTimeFormat)] stri
         /// <param name="provider">An object that supplies culture-specific formatting information.</param>
         /// <returns>A string representation of value of the current <see cref="EssentialsTime"/> object as specified by <paramref name="format"/> and <paramref name="provider"/>.</returns>
         public string ToString([StringSyntax(StringSyntaxAttribute.DateTimeFormat)] string? format, IFormatProvider? provider) {
-            return DateTimeOffset.ToString(format, provider);
+            return string.IsNullOrWhiteSpace(format) ? Iso8601 : DateTimeOffset.ToString(format, provider);
         }
 
         /// <summary>

src/TestProject1/Time/EssentialsDateTests.cs

@@ -13,8 +13,9 @@ public void ToStringDefault() {
 
         EssentialsDate date = new(2024, 3, 27);
 
-        Assert.AreEqual("2024-03-27", date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture));
-        Assert.AreEqual("2024-03-27", date.ToString("yyyy-MM-dd", CultureInfo.GetCultureInfo("da-DK")));
+        Assert.AreEqual("2024-03-27", date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture), "#1");
+        Assert.AreEqual("2024-03-27", date.ToString("yyyy-MM-dd", CultureInfo.GetCultureInfo("da-DK")), "#2");
+        Assert.AreEqual("2024-03-27", $"{date}", "#3");
 
     }
 

src/TestProject1/Time/EssentialsTimeTests.cs

@@ -13,7 +13,8 @@ public void ToStringDefault() {
 
         EssentialsTime time = new(2024, 3, 27, 12, 0, 0, TimeZoneInfo.Utc);
 
-        Assert.AreEqual("2024-03-27T12:00:00.000Z", time.ToString());
+        Assert.AreEqual("2024-03-27T12:00:00.000Z", time.ToString(), "#1");
+        Assert.AreEqual("2024-03-27T12:00:00.000Z", $"{time}", "#2");
 
     }
 

src/UnitTestProject1/Time/Time/EssentialsDateTests.cs

@@ -235,6 +235,17 @@ public void Max() {
 
         }
 
+        [TestMethod]
+        public void ToStringDefault() {
+
+            EssentialsDate date = new EssentialsDate(2024, 4, 7);
+
+            Assert.AreEqual("2024-04-07", date.ToString());
+            Assert.AreEqual("2024-04-07", $"{date}");
+            Assert.AreEqual("2024-04-07", $"{date:yyyy-MM-dd}");
+
+        }
+
     }
 
 }