Add tests to TestTrim() method for changes made to coreclr Trim* family

src/NuGet.config

@@ -1,16 +1,15 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <configuration>
   <!-- NOTE: Leave this file here and keep it in sync with list in dir.props. -->
   <!-- The command-line doesn't need it, but the IDE does.                    -->
+  <config>
+    <add key="repositoryPath" value="..\packages" />
+  </config>
   <packageSources>
-    <clear/>
     <add key="myget.org dotnet-core" value="https://www.myget.org/F/dotnet-core/" />
     <add key="myget.org dotnet-coreclr" value="https://www.myget.org/F/dotnet-coreclr/" />
     <add key="myget.org dotnet-corefxtestdata" value="https://www.myget.org/F/dotnet-corefxtestdata/" />
     <add key="myget.org dotnet-buildtools" value="https://www.myget.org/F/dotnet-buildtools/" />
     <add key="nuget.org" value="https://www.nuget.org/api/v2/" />
   </packageSources>
-  <config>
-    <add key="repositoryPath" value="..\packages" />
-  </config>
 </configuration>

src/System.Runtime/ref/System.Runtime.cs

@@ -1617,6 +1617,11 @@ public void CopyTo(int sourceIndex, char[] destination, int destinationIndex, in
         public string ToUpper() { return default(string); }
         public string ToUpperInvariant() { return default(string); }
         public string Trim() { return default(string); }
+        public string TrimStart() { return default(string); }
+        public string TrimEnd() { return default(string); }
+        public string Trim(char trimChars) { return default(string); }
+        public string TrimStart(char trimChars) { return default(string); }
+        public string TrimEnd(char trimChars) { return default(string); }
         public string Trim(params char[] trimChars) { return default(string); }
         public string TrimEnd(params char[] trimChars) { return default(string); }
         public string TrimStart(params char[] trimChars) { return default(string); }

src/System.Runtime/tests/System.Runtime.Tests.csproj

@@ -111,6 +111,11 @@
   </ItemGroup>
   <ItemGroup>
     <!-- Compile tests against the System.Runtime contract, but copy our local-built implementation for testing -->
+    <ProjectReference Include="..\ref\System.Runtime.csproj">
+       <ReferenceOutputAssembly>true</ReferenceOutputAssembly>
+       <OutputItemType>None</OutputItemType>
+       <CopyToOutputDirectory>Never</CopyToOutputDirectory>
+    </ProjectReference>
     <ProjectReference Include="..\src\System.Runtime.CoreCLR.csproj">
       <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
       <OutputItemType>Content</OutputItemType>

src/System.Runtime/tests/System/String.cs

@@ -1519,17 +1519,68 @@ public static void TestTrim()
         s = ". Foo .".Trim('.');
         Assert.Equal(" Foo ", s);
 
+        s = "..Foo.".Trim('.');
+        Assert.Equal("Foo", s);
+
+        s = ".Foo .".Trim('.');
+        Assert.Equal("Foo ", s);
+
         s = "  Foo  ".TrimStart();
         Assert.Equal("Foo  ", s);
 
         s = ". Foo .".TrimStart('.');
         Assert.Equal(" Foo .", s);
 
+        s = "..Foo.".TrimStart('.');
+        Assert.Equal("Foo.", s);
+
+        s = ".Foo .".TrimStart('.');
+        Assert.Equal("Foo .", s);
+
         s = "  Foo  ".TrimEnd();
         Assert.Equal("  Foo", s);
 
         s = ". Foo .".TrimEnd('.');
         Assert.Equal(". Foo ", s);
+
+        s = "..Foo.".TrimEnd('.');
+        Assert.Equal("..Foo", s);
+
+        s = ".Foo .".TrimEnd('.');
+        Assert.Equal(".Foo ", s);
+
+        s = ".  Foo  .".Trim('.', 'F');
+        Assert.Equal("  Foo  ", s);
+
+        s = ".Foo  .".Trim('.', 'F');
+        Assert.Equal("oo  ", s);
+
+        s = "..  FFoo  .".TrimStart('.', 'F');
+        Assert.Equal("  FFoo  .", s);
+
+        s = "..FFoo  .".TrimStart('.', 'F');
+        Assert.Equal("oo  .", s);
+
+        s = "..  FFoo  ..".TrimEnd('.','o');
+        Assert.Equal("..  FFoo  ", s);
+
+        s = "..  FFoo..".TrimEnd('.', 'o');
+        Assert.Equal("..  FF", s);
+
+        s = ".Foo  .".Trim('.', 'F', 'x');
+        Assert.Equal("oo  ", s);
+
+        s = "..  FFoo  .".TrimStart('.', 'F', 'x');
+        Assert.Equal("  FFoo  .", s);
+
+        s = "..  FFoo  ..".TrimEnd('.', 'o', 'x');
+        Assert.Equal("..  FFoo  ", s);
+
+        s = ".xFoo  .".Trim('.', 'F', 'x');
+        Assert.Equal("oo  ", s);
+
+        s = ".Fxoo  .".Trim('.', 'F', 'x');
+        Assert.Equal("oo  ", s);
     }
 
     [Fact]