set DISPLAY in tox.ini for tk tests with window

Makefile

@@ -53,8 +53,15 @@ clean-test: ## remove test and coverage artifacts
 lint: ## check style with flake8
 	flake8 flatland tests
 
+test:	export DISPLAY = :0
 test: ## run tests quickly with the default Python
-	export DISPLAY=:0.0
+	echo "$$DISPLAY"
+	py.test
+
+
+jw: 	export DISPLAY = :0.0
+jw:
+	echo "$$DISPLAY"
 	py.test
 
 test-all: ## run tests on every Python version with tox

flatland/utils/graphics_pil.py

@@ -86,7 +86,7 @@ class PILGL(GraphicsLayer):
     def create_layer(self, iLayer=0):
         if len(self.layers) <= iLayer:
             for i in range(len(self.layers), iLayer+1):
-                if i==0:
+                if i == 0:
                     opacity = 255  # "bottom" layer is opaque (for rails)
                 else:
                     opacity = 0   # subsequent layers are transparent

tox.ini

@@ -28,6 +28,7 @@ commands = make coverage
 [testenv]
 setenv =
     PYTHONPATH = {toxinidir}
+    DISPLAY = :0
 deps =
     -r{toxinidir}/requirements_dev.txt
 ; If you want to make tox run the tests with the same versions, create a