feat(*): Add SystemTime.Now documentation to readme

Creek.HelpfulExtensions/Creek.HelpfulExtensions.csproj

@@ -19,8 +19,8 @@
     <PackageLicenseFile>LICENSE</PackageLicenseFile>
     <RepositoryType>git</RepositoryType>
     <PackageTags>creek</PackageTags>
-    <Version>1.1.0</Version>
+    <Version>1.2.0</Version>
-    <AssemblyVersion>1.1.0.0</AssemblyVersion>
+    <AssemblyVersion>1.2.0.0</AssemblyVersion>
   </PropertyGroup>
 
   <ItemGroup>

Creek.HelpfulExtensions/SystemTime.cs

@@ -0,0 +1,18 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Creek.HelpfulExtensions
+{
+    public static class SystemTime
+    {
+        /// <summary>
+        /// This method exposes DateTime.Now as an instance of a function, that can be replaced in tests.
+        /// </summary>
+#pragma warning disable S1104 // Fields should not have public accessibility
+#pragma warning disable S2223 // Non-constant static fields should not be visible
+        public static Func<DateTime> Now = () => DateTime.Now;
+#pragma warning restore S2223 // Non-constant static fields should not be visible
+#pragma warning restore S1104 // Fields should not have public accessibility
+    }
+}

README.md

@@ -40,3 +40,31 @@ foreach (var (item, index) in list.WithIndex())
     // ...
 }
 ```
+
+## DateTime Extensions
+
+### SystemTime.Now
+
+This is technically not an extension, but fits well in this package. It's taken from [this blog](https://lostechies.com/jimmybogard/2008/11/09/systemtime-versus-isystemclock-dependencies-revisited/). This method exposes DateTime.Now as an instance of a function, that can be replaced in tests.
+
+If you want to replace SystemTime.Now in a test you can do it like this:
+
+```csharp
+[Test]
+public void Should_test_something_here()
+{
+    var systemTimeDate = new DateTime(2021, 9, 2);
+    SystemTime.Now = () => new DateTime(2021, 9, 2);
+
+    DateTime dateTimeToBeTested = systemTimeDate;
+
+    // ...
+}
+```
+
+You can also set SystemTime.Now to any function that returns a DateTime:
+
+```csharp
+var startDate = new DateTime(2021, 9, 2);
+SystemTime.Now = () => startDate.AddDays(2);
+```