Why am I getting a Key Error when I run app_tests.py?

import datetime

from flask.ext.bcrypt import generate_password_hash
from flask.ext.login import UserMixin

from peewee import *


DATABASE = SqliteDatabase('tacocat.db')


class User(UserMixin, Model):
    """A taco cat customer"""
    username = CharField(unique=True)
    email = CharField(unique=True)
    password = CharField(max_length=100)
    is_admin = BooleanField(default=False)

    class Meta:
        database = DATABASE

    @classmethod
    def create_user(cls, username, email, password, admin=False):
        try:
            with DATABASE.transaction():
                cls.create(
                    username=username,
                    email=email,
                    password=generate_password_hash(password),
                    is_admin=admin)
        except IntegrityError:
            raise ValueError("User already exists")


class Taco(Model):
    """Taco creation by the customer"""
    timestamp = DateTimeField(default=datetime.datetime.now)
    user = ForeignKeyField(
        rel_model=User,
        related_name='tacos'
    )
    protein = CharField(max_length=100)
    cheese = BooleanField()
    shell = CharField(max_length=100)
    extras = TextField()

    class Meta:
        database = DATABASE
        order_by = ('-timestamp')


def initialize():
    DATABASE.connect()
    DATABASE.create_tables([User, Taco], safe=True)
    DATABASE.close()

import datetime

from flask.ext.bcrypt import generate_password_hash
from flask.ext.login import UserMixin

from peewee import *


DATABASE = SqliteDatabase('tacocat.db')


class User(UserMixin, Model):
    """A taco cat customer"""
    username = CharField(unique=True)
    email = CharField(unique=True)
    password = CharField(max_length=100)
    is_admin = BooleanField(default=False)

    class Meta:
        database = DATABASE

    @classmethod
    def create_user(cls, username, email, password, admin=False):
        try:
            with DATABASE.transaction():
                cls.create(
                    username=username,
                    email=email,
                    password=generate_password_hash(password),
                    is_admin=admin)
        except IntegrityError:
            raise ValueError("User already exists")


class Taco(Model):
    """Taco creation by the customer"""
    timestamp = DateTimeField(default=datetime.datetime.now)
    user = ForeignKeyField(
        rel_model=User,
        related_name='tacos'
    )
    protein = CharField(max_length=100)
    cheese = BooleanField()
    shell = CharField(max_length=100)
    extras = TextField()

    class Meta:
        database = DATABASE
        order_by = ('-timestamp')


def initialize():
    DATABASE.connect()
    DATABASE.create_tables([User, Taco], safe=True)
    DATABASE.close()

from flask_wtf import Form
from wtforms import StringField, PasswordField, TextAreaField, BooleanField
from wtforms.validators import (DataRequired, Regexp, ValidationError, Email,
                                Length, EqualTo)

from models import User

def name_exists(form, field):
    """Register fails because it is a username that already exists in the database"""
    if User.select().where(User.username == field.data).exists():
        raise ValidationError('User with that name already exists.')


def email_exists(form, field):
    """Register fails because it is an email that already exists in the database"""
    if User.select().where(User.email == field.data).exists():
        raise ValidationError('User with that email already exists.')


class RegisterForm(Form):
    """Creates a form to register a new user"""
    username = StringField(
        'Username',
        validators=[
            DataRequired(),
            Regexp(
                r'^[a-zA-Z0-9_]+$',
                message=("Username should be one word, letters, "
                         "numbers, and underscores only.")
            ),
            name_exists
        ])
    email = StringField(
        'Email',
        validators=[
            DataRequired(),
            Email(),
            email_exists
        ])
    password = PasswordField(
        'Password',
        validators=[
            DataRequired(),
            Length(min=2),
            EqualTo('password2', message='Passwords must match')
        ])
    password2 = PasswordField(
        'ConfirmPassword',
        validators=[DataRequired()]
    )


class LoginForm(Form):
    """Creates a form to log a user in"""
    email = StringField('Email', validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])


class TacoForm(Form):
    """Creates a form to order a taco"""
    protein = StringField("Meat? Chicken? Pork? Veggie?", validator=[DataRequired()])
    cheese = BooleanField("Cheese", default=True)
    shell = StringField("Corn? Wheat? Crispy? Soft?", validator=[DataRequired()])
    extras = TextAreaField("Anything else?", validator=[DataRequired()])