Fix constraints bug.

Add constraints unittests.
Update invalid words.

.vscode/launch.json

@@ -20,6 +20,17 @@
             ],
             "jinja": true,
             "justMyCode": true
+        },
+        {
+            "name": "Python: Debug Tests",
+            "type": "python",
+            "request": "launch",
+            "program": "${file}",
+            "purpose": [
+                "debug-test"
+            ],
+            "console": "integratedTerminal",
+            "justMyCode": false
         }
     ]
 }

.vscode/settings.json

@@ -0,0 +1,11 @@
+{
+    "python.testing.unittestArgs": [
+        "-v",
+        "-s",
+        ".",
+        "-p",
+        "test*.py"
+    ],
+    "python.testing.pytestEnabled": false,
+    "python.testing.unittestEnabled": true
+}