DateTime.Now vs DateTime.UtcNow: retarget net10.0, bump test packages, add Unspecified conversion tests (#2150)

- Both projects net6.0 -> net10.0
- Microsoft.NET.Test.Sdk 16.11.0 -> 18.9.0, MSTest 2.2.7 -> 4.3.3, coverlet.collector 3.1.0 -> 10.0.1
- Two tests pinning the DateTimeKind.Unspecified asymmetry: ToLocalTime() treats an
  unspecified value as UTC, ToUniversalTime() treats it as local. Written offset-agnostic
  so they hold in a UTC CI container.

Author: vladimir-pecanac-main

dotnet-datetime/DateTimeNowVsDateTimeUtcNow/DateTimeNow.Tests/DateTimeNow.Tests.csproj

@@ -1,17 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <Nullable>enable</Nullable>
 
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.11.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="2.2.7" />
-    <PackageReference Include="MSTest.TestFramework" Version="2.2.7" />
-    <PackageReference Include="coverlet.collector" Version="3.1.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.9.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="4.3.3" />
+    <PackageReference Include="MSTest.TestFramework" Version="4.3.3" />
+    <PackageReference Include="coverlet.collector" Version="10.0.1" />
   </ItemGroup>
 
 </Project>

dotnet-datetime/DateTimeNowVsDateTimeUtcNow/DateTimeNow.Tests/DateTimeTests.cs

@@ -56,5 +56,27 @@ public void LocalDate_ConvertToUTC_ReturnsUTCDate()
 
             Assert.IsTrue(now.Kind == DateTimeKind.Local && utc.Kind == DateTimeKind.Utc);
         }
+
+        [TestMethod]
+        public void UnspecifiedDate_WhenConvertedToLocalTime_IsTreatedAsUtc()
+        {
+            var value = new DateTime(2022, 1, 9, 14, 34, 42);
+
+            var unspecified = DateTime.SpecifyKind(value, DateTimeKind.Unspecified);
+            var asUtc = DateTime.SpecifyKind(value, DateTimeKind.Utc);
+
+            Assert.AreEqual(asUtc.ToLocalTime(), unspecified.ToLocalTime());
+        }
+
+        [TestMethod]
+        public void UnspecifiedDate_WhenConvertedToUniversalTime_IsTreatedAsLocal()
+        {
+            var value = new DateTime(2022, 1, 9, 14, 34, 42);
+
+            var unspecified = DateTime.SpecifyKind(value, DateTimeKind.Unspecified);
+            var asLocal = DateTime.SpecifyKind(value, DateTimeKind.Local);
+
+            Assert.AreEqual(asLocal.ToUniversalTime(), unspecified.ToUniversalTime());
+        }
     }
 }

dotnet-datetime/DateTimeNowVsDateTimeUtcNow/DateTimeNowVsDateTimeUtcNow/DateTimeNowVsDateTimeUtcNow.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>