@@ -55,9 +55,17 @@ jobs:
         if: ${{ matrix.os == 'windows' }}
         run: |
           python -m pythonnet.find_libpython --export | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
-  
-      - name: Python Tests
-        run: pytest
+
+      - name: Python Tests (Mono)
+        if: ${{ matrix.os != 'windows' }}
+        run: pytest --runtime mono
+
+      - name: Python Tests (.NET Core)
+        run: pytest --runtime netcore
+
+      - name: Python Tests (.NET Framework)
+        if: ${{ matrix.os == 'windows' }}
+        run: pytest --runtime netfx
 
       - name: Embedding tests
         run: dotnet test --runtime any-${{ matrix.platform }} src/embed_tests/
 
@@ -1,3 +1,9 @@
 [build-system]
 requires = ["setuptools>=42", "wheel", "pycparser"]
 build-backend = "setuptools.build_meta"
+
+[tool.pytest.ini_options]
+xfail_strict = true
+testpaths = [
+    "tests",
+]
@@ -1,14 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net5.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <GenerateRuntimeConfigurationFiles>true</GenerateRuntimeConfigurationFiles>
   </PropertyGroup>
 
   <ItemGroup>
     <ProjectReference Include="..\runtime\Python.Runtime.csproj" />
   </ItemGroup>
-
-  <Target Name="AfterBuild">
-    <Copy SourceFiles="$(TargetAssembly)" DestinationFolder="$(MSBuildThisFileDirectory)..\tests\fixtures" />
-  </Target>
 </Project>
@@ -0,0 +1,101 @@
+# -*- coding: utf-8 -*-
+# TODO: move tests one out of src to project root.
+# TODO: travis has numpy on their workers. Maybe add tests?
+
+"""Helpers for testing."""
+
+import ctypes
+import os
+import sys
+import sysconfig
+from subprocess import check_call
+from tempfile import mkdtemp
+import shutil
+
+import pytest
+
+from pythonnet import set_runtime
+
+# Add path for `Python.Test`
+cwd = os.path.dirname(__file__)
+fixtures_path = os.path.join(cwd, "fixtures")
+sys.path.append(fixtures_path)
+
+def pytest_addoption(parser):
+    parser.addoption(
+        "--runtime",
+        action="store",
+        default="default",
+        help="Must be one of default, netcore, netfx and mono"
+    )
+
+def pytest_configure(config):
+    global bin_path
+    runtime_opt = config.getoption("runtime")
+
+    test_proj_path = os.path.join(cwd, "..", "src", "testing")
+
+    if runtime_opt not in ["netcore", "netfx", "mono", "default"]:
+        raise RuntimeError(f"Invalid runtime: {runtime_opt}")
+
+    bin_path = mkdtemp()
+
+    # tmpdir_factory.mktemp(f"pythonnet-{runtime_opt}")
+
+    fw = "net5.0" if runtime_opt == "netcore" else "netstandard2.0"
+
+    check_call(["dotnet", "publish", "-f", fw, "-o", bin_path, test_proj_path])
+
+    sys.path.append(bin_path)
+
+    if runtime_opt == "default":
+        pass
+    elif runtime_opt == "netfx":
+        from clr_loader import get_netfx
+        runtime = get_netfx()
+        set_runtime(runtime)
+    elif runtime_opt == "mono":
+        from clr_loader import get_mono
+        runtime = get_mono()
+        set_runtime(runtime)
+    elif runtime_opt == "netcore":
+        from clr_loader import get_coreclr
+        rt_config_path = os.path.join(bin_path, "Python.Test.runtimeconfig.json")
+        runtime = get_coreclr(rt_config_path)
+        set_runtime(runtime)
+
+    import clr
+    clr.AddReference("Python.Test")
+    clr.AddReference("System")
+    clr.AddReference("System.Collections")
+    clr.AddReference("System.Data")
+    clr.AddReference("System.Xml")
+
+
+def pytest_unconfigure(config):
+    global bin_path
+    shutil.rmtree(bin_path)
+
+def pytest_report_header(config):
+    """Generate extra report headers"""
+    # FIXME: https://github.com/pytest-dev/pytest/issues/2257
+    is_64bits = sys.maxsize > 2**32
+    arch = "x64" if is_64bits else "x86"
+    ucs = ctypes.sizeof(ctypes.c_wchar)
+    libdir = sysconfig.get_config_var("LIBDIR")
+    shared = bool(sysconfig.get_config_var("Py_ENABLE_SHARED"))
+
+    header = ("Arch: {arch}, UCS: {ucs}, LIBDIR: {libdir}, "
+              "Py_ENABLE_SHARED: {shared}".format(**locals()))
+    return header
+
+
+@pytest.fixture()
+def filepath():
+    """Returns full filepath for file in `fixtures` directory."""
+
+    def make_filepath(filename):
+        # http://stackoverflow.com/questions/18011902/parameter-to-a-fixture
+        return os.path.join(fixtures_path, filename)
+
+    return make_filepath