Django Integrated Test Passing When it Should Fail

Question

I'm in the process of creating an assessment system using Django; however, I have an integrated test that passes and I'm not sure as to why (it should be failing). In the test, I set the grade field of the bobenrollment object to "Excellent". As you can see from the models below, the Enrollment model doesn't have a grade field (none of the models do). I was under the impression that dot notation of model objects would access the model fields (I'm probably incorrect about this). I don't want to write ineffective tests, so I would like to know what makes this test pass and what I should do to make it break. Thanks!

class ClassAndSemesterModelTest(TestCase):

    def add_two_classes_to_semester_add_two_students_to_class(self):
        first_semester = Semester.objects.create(text='201530')
        edClass = EdClasses.objects.create(name='EG 5000') 
        edClass2 = EdClasses.objects.create(name='EG 6000')

        first_semester.classes.add(edClass)
        first_semester.classes.add(edClass2)

        bob = Student.objects.create(name="Bob DaBuilder")
        jane = Student.objects.create(name="Jane Doe")

        bobenrollment = Enrollment.objects.create(student=bob, edclass=edClass)
        janeenrollment = Enrollment.objects.create(student=jane,edclass=edClass)
        bobenrollment2 = Enrollment.objects.create(student=bob,edclass=edClass2)
        janeenrollment2 = Enrollment.objects.create(student=jane,edclass=edClass2)

    def test_students_link_to_enrollments(self):
        self.add_two_classes_to_semester_add_two_students_to_class()
        edclass1 = EdClasses.objects.get(name="EG 5000")
        bob = Student.objects.get(name="Bob DaBuilder")
        #The three lines below are the subject of my question
        bobenrollment = Enrollment.objects.get(edclass=edclass1, student=bob)
        bobenrollment.grade = "Excellent"
        self.assertEqual(bobenrollment.grade, "Excellent")

And the models below:

from django.db import models

class Student(models.Model):
    name = models.TextField(default="") 

    def __str__(self):
        return self.name
    #TODO add models

class EdClasses(models.Model):
    name = models.TextField(default='')
    students = models.ManyToManyField(Student, through="Enrollment")

    def __str__(self):
        return self.name

class Semester(models.Model):
    text = models.TextField(default='201530')
    classes = models.ManyToManyField(EdClasses) 
    def __str__(self):
        return self.text

class Enrollment(models.Model):
    student = models.ForeignKey(Student)
    edclass = models.ForeignKey(EdClasses)

Requirements.txt

beautifulsoup4==4.4.1
Django==1.5.4
ipython==3.1.0
LiveWires==2.0
nose==1.3.3
Pillow==2.7.0
projectname==0.1
pyperclip==1.5.11
pytz==2015.2
requests==2.10.0
selenium==2.53.6
six==1.9.0
South==1.0.2
swampy==2.1.7
virtualenv==1.11.5

Answer 1

I was under the impression that dot notation of model objects would access the model fields (I'm probably incorrect about this)

You're correct about this. What you're not taking into account is the fact that you can dynamically add properties to python objects. For instance:

In [1]: class MyClass():
   ...:     pass
   ...:
In [2]: a = MyClass()
In [3]: a.im_a_property = 'hello'
In [4]: print a.im_a_property
hello

As you can see, the a instance will have the im_a_propery property even though it's not defined by the class. The same applies for the following line in your code:

bobenrollment.grade = "Excellent"

Django models override this behavior so you can seamlessly get DB values as properties of your model instance, but the instance is just a regular python object.

If you want to test the grade property gets saved correctly, you should modify your test to add the value of grade when creating the record and making sure the instance you assert against is the one you read from your DB (i.e. not modifying it beforehand).