Add Windows to the GitHub Actions CI test matrix (#539)

* Add Windows, expect a test to fail due to screen size

* Remove unreliable assertion, it fails when the host machine is different

* Clarify comment

.github/workflows/test-with-edm.yml

@@ -15,9 +15,15 @@ jobs:
   test-with-edm:
     strategy:
       matrix:
-        os: [macos-latest]
+        os: [macos-latest, windows-latest]
         toolkit: ['pyqt', 'pyqt5', 'pyside2', 'wx']
     runs-on: ${{ matrix.os }}
+    env:
+      # Set root directory, mainly for Windows, so that the EDM Python
+      # environment lives in the same drive as the cloned source. Otherwise
+      # 'pip install' raises an error while trying to compute
+      # relative path between the site-packages and the source directory.
+      EDM_ROOT_DIRECTORY: ${{ github.workspace }}/.edm
     steps:
       - uses: actions/checkout@v2
       - name: Cache EDM packages

enable/tests/test_component_editor.py

@@ -57,9 +57,5 @@ def test_initial_component_with_item_size(self):
 
         size = get_dialog_size(ui.control)
 
-        # leave a few pixel of margin for wx
         self.assertGreater(size[0], ITEM_WIDTH-1)
-        self.assertLess(size[0], ITEM_WIDTH+30)
-
         self.assertGreater(size[1], ITEM_HEIGHT-1)
-        self.assertLess(size[1], ITEM_HEIGHT+30)