Add tests to the admin

{{cookiecutter.repo_name}}/{{cookiecutter.repo_name}}/users/admin.py

@@ -15,6 +15,11 @@ class MyUserChangeForm(UserChangeForm):
 
 
 class MyUserCreationForm(UserCreationForm):
+
+    error_message = UserCreationForm.error_messages.update({
+        'duplicate_username': 'This username has already been taken.'
+    })
+
     class Meta(UserCreationForm.Meta):
         model = User
 

{{cookiecutter.repo_name}}/{{cookiecutter.repo_name}}/users/tests/test_admin.py

@@ -0,0 +1,42 @@
+from django import forms
+
+from test_plus.test import TestCase
+
+from ..admin import MyUserCreationForm
+
+
+class TestMyUserCreationForm(TestCase):
+
+    def setUp(self):
+        self.user = self.make_user()
+
+    def test_clean_username_success(self):
+        # Instantiate the form with a new username
+        form = MyUserCreationForm({
+            'username': 'alamode',
+            'password1': '123456',
+            'password2': '123456',
+        })
+        # Run is_valid() to trigger the validation
+        valid = form.is_valid()
+        self.assertTrue(valid)
+
+        # Run the actual clean_username method
+        username = form.clean_username()
+        self.assertEqual('alamode', username)
+
+    def test_clean_username_false(self):
+        # Instantiate the form with the same username as self.user
+        form = MyUserCreationForm({
+            'username': self.user.username,
+            'password1': '123456',
+            'password2': '123456',
+        })
+        # Run is_valid() to trigger the validation, which is going to fail
+        # because the username is already taken
+        valid = form.is_valid()
+        self.assertFalse(valid)
+
+        # The form.errors dict should contain a single error called 'username'
+        self.assertTrue(len(form.errors) == 1)
+        self.assertTrue('username' in form.errors)