Use the windows "gotchcas" fix for example tests

Apply the fix from @chrizzFTD where we invoke the entry point using
module exec mode on a ``__main__.py`` and import the
``test_example::`main()` from within that entry point script.

examples/__main__.py

@@ -0,0 +1,11 @@
+"""
+Needed in windows.
+This needs to be the main program as it will be
+called '__mp_main__' by the multiprocessing module
+
+"""
+if __name__ == '__main__':
+    import multiprocessing
+    multiprocessing.freeze_support()
+    from . import test_example
+    test_example.tractor.run(test_example.main, start_method='spawn')

examples/a_trynamic_first_scene.py

@@ -1,5 +1,5 @@
+import platform
 import tractor
-from functools import partial
 
 _this_module = __name__
 the_line = 'Hi my name is {}'

tests/test_docs_examples.py

@@ -6,7 +6,7 @@ import os
 import sys
 import subprocess
 import platform
-import pprint
+import shutil
 
 import pytest
 
@@ -21,19 +21,45 @@ def confdir():
 
 
 @pytest.fixture
-def run_example_in_subproc(loglevel, testdir, arb_addr):
+def examples_dir(confdir):
+    return os.path.join(confdir, 'examples')
+
+
+@pytest.fixture
+def run_example_in_subproc(loglevel, testdir, arb_addr, examples_dir):
 
     @contextmanager
     def run(script_code):
+        kwargs = dict()
+
+        if platform.system() == 'Windows':
+            # on windows we need to create a special __main__.py which will
+            # be executed with ``python -m __main__.py`` on windows..
+            shutil.copyfile(
+                os.path.join(examples_dir, '__main__.py'),
+                os.path.join(str(testdir), '__main__.py')
+            )
+
+            # drop the ``if __name__ == '__main__'`` guard
+            script_code = '\n'.join(script_code.splitlines()[:-4])
+            script_file = testdir.makefile('.py', script_code)
+
+            # without this, tests hang on windows forever
+            kwargs['creationflags'] = subprocess.CREATE_NEW_PROCESS_GROUP
+
+            # run the "libary module" as a script
+            cmdargs = [
+                sys.executable,
+                '-m',
+                # use the "module name" of this "package"
+                'test_example'
+            ]
+        else:
             script_file = testdir.makefile('.py', script_code)
             cmdargs = [
                 sys.executable,
                 str(script_file),
             ]
-        kwargs = dict()
-        if platform.system() == 'Windows':
-            # without this, tests hang on windows forever
-            kwargs['creationflags'] = subprocess.CREATE_NEW_PROCESS_GROUP
 
         proc = testdir.popen(
             cmdargs,
@@ -49,8 +75,8 @@ def run_example_in_subproc(loglevel, testdir, arb_addr):
     yield run
 
 
-def test_a_trynamic_first_scene(confdir, run_example_in_subproc):
-    ex_file = os.path.join(confdir, 'examples', 'a_trynamic_first_scene.py')
+def test_example(examples_dir, run_example_in_subproc):
+    ex_file = os.path.join(examples_dir, 'a_trynamic_first_scene.py')
     with open(ex_file, 'r') as ex:
         code = ex.read()