feat: restore original framework selection behavor

Author: dupdob

src/Stryker.Core/Stryker.Core.UnitTest/Initialisation/InputFileResolverTests.cs

@@ -1143,10 +1143,10 @@ public void ShouldSelectFrameworkBasedOnTestProject(string testFrameworks
         result.TestProjectsInfo.AnalyzerResults.First().TargetFramework.ShouldBe(expectedTestFramework);
     }
 
-    // Stryker will ignore NetFramework target when runnning on non windows platforms
+    // Stryker accepts netframework targert when running on Windows
     [TestMethodWithIgnoreIfSupport]
     [IgnoreIf(nameof(Is.NotWindows))]
-    [DataRow("net462,netcoreapp3.0", "net461,netcoreapp2.0", null, "net462", "net461")]
+    [DataRow("net462", "net461", null, "net462", "net461")]
     public void ShouldSelectFrameworkBasedOnTestProjectOnWindows(string testFrameworks
         , string projectFrameworks
         , string targetFramework

src/Stryker.Core/Stryker.Core/Initialisation/MutableProjectTree.cs

@@ -58,10 +58,9 @@ public void KeepOnlyOneTarget(string optionsTargetFramework)
         }
 
         var mutableProjectTargets = Targets.Where(t => t.IsValidTarget);
-        // on non windows platform, keep first non netframework target
-        // on Windows, keep first netframework target if any, otherwise keep first valid target
-        targetToKeep = mutableProjectTargets.FirstOrDefault( t => OperatingSystem.IsWindows() == t.ProjectTarget.TargetsFullFramework()) ??
-                       mutableProjectTargets.FirstOrDefault();
+        // keep the first non netframework target otherwise pick the first one when running on Windows OS
+        targetToKeep = mutableProjectTargets.FirstOrDefault( t => !t.ProjectTarget.TargetsFullFramework()) ??
+                       mutableProjectTargets.FirstOrDefault(_ => OperatingSystem.IsWindows());
         Targets.Clear();
         if (targetToKeep == null)
         {