Draft: add Draft Layer unit tests

Also create a test `Layer` in the `draft_test_objects` script.

src/Mod/Draft/drafttests/draft_test_objects.py

@@ -574,6 +574,40 @@ def _create_objects(doc=None,
     t_xpos = 17000
     t_ypos = 2200
     _set_text(["Mirror"], Vector(t_xpos, t_ypos, 0))
+
+    _msg(16 * "-")
+    _msg("Layer")
+    layer = Draft.make_layer("Custom layer",
+                             line_color=(0.33, 0.0, 0.49),
+                             shape_color=(0.56, 0.89, 0.56),
+                             line_width=4,
+                             transparency=50)
+    cube = doc.addObject('Part::Box')
+    cube.Length = 350
+    cube.Width = 300
+    cube.Height = 250
+    cube.Placement.Base = Vector(14000, 5500, 0)
+
+    cone = doc.addObject('Part::Cone')
+    cone.Radius1 = 400
+    cone.Height = 600
+    cone.Angle = 270
+    cone.Placement.Base = Vector(15000, 6000, 0)
+
+    sphere = doc.addObject('Part::Sphere')
+    sphere.Radius = 450
+    sphere.Angle1 = -45
+    sphere.Angle2 = 45
+    sphere.Angle3 = 300
+    sphere.Placement.Base = Vector(14000, 7000, 0)
+
+    layer.Proxy.addObject(layer, cube)
+    layer.Proxy.addObject(layer, cone)
+    layer.Proxy.addObject(layer, sphere)
+
+    t_xpos = 14000
+    t_ypos = 5000
+    _set_text(["Layer"], Vector(t_xpos, t_ypos, 0))
     doc.recompute()
 
 

src/Mod/Draft/drafttests/test_creation.py

@@ -348,6 +348,19 @@ class DraftCreation(unittest.TestCase):
         self.doc.recompute()
         self.assertTrue(obj, "'{}' failed".format(operation))
 
+    def test_layer(self):
+        """Create a layer, and add a rectangle to it."""
+        operation = "Draft Layer"
+        _msg("  Test '{}'".format(operation))
+        length = 5
+        width = 2
+        _msg("  length={0}, width={1}".format(length, width))
+        rect = Draft.make_rectangle(length, width)
+
+        obj = Draft.make_layer()
+        obj.Proxy.addObject(obj, rect)
+        self.assertTrue(obj, "'{}' failed".format(operation))
+
     def tearDown(self):
         """Finish the test.