add linux test project

Author: Oren Novotny

Rx.NET/Integration/LinuxTests/LinuxTests.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="MSBuild.Sdk.Extras">
+  <PropertyGroup>
+    <TargetFrameworks>netcoreapp3.0;netcoreapp2.1</TargetFrameworks>
+    <NoWarn>$(NoWarn);CS0618</NoWarn>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Content Include="..\..\Source\tests\Tests.System.Reactive\xunit.runner.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+    <Compile Include="..\..\Source\tests\Tests.System.Reactive\**\*.cs" 
+             Exclude="..\..\Source\tests\Tests.System.Reactive\obj\**" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.0.0-preview-20181205-02" />    
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1" />
+    <PackageReference Include="System.Reactive" Version="4.2.0-preview.63" />
+    <PackageReference Include="Microsoft.Reactive.Testing" Version="4.2.0-preview.63" />
+    <PackageReference Include="System.Reactive.Observable.Aliases Version="4.2.0-preview.63" />
+  </ItemGroup>
+</Project>