diff --git a/Makefile b/Makefile
index b107c31..c189921 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-checkfiles = aerich/ tests/
+checkfiles = aerich/ tests/ conftest.py
 black_opts = -l 100 -t py38
 py_warn = PYTHONDEVMODE=1
 MYSQL_HOST ?= "127.0.0.1"
diff --git a/README.rst b/README.rst
index cb5f536..9093327 100644
--- a/README.rst
+++ b/README.rst
@@ -104,6 +104,10 @@ Init db
     Success create app migrate location ./migrations/models
     Success generate schema for app "models"
 
+.. note::
+
+    If your Tortoise-ORM app is not default ``models``, you must specify ``--app`` like ``aerich --app other_models init-db``.
+
 Update models and make migrate
 ------------------------------
 
diff --git a/aerich/cli.py b/aerich/cli.py
index 30e4d23..ae2bf86 100644
--- a/aerich/cli.py
+++ b/aerich/cli.py
@@ -12,6 +12,7 @@
 
 from aerich.migrate import Migrate
 from aerich.utils import get_app_connection, get_app_connection_name, get_tortoise_config
+
 from . import __version__
 from .models import Aerich
 
@@ -158,7 +159,7 @@ def history(ctx):
 )
 @click.pass_context
 async def init(
-        ctx: Context, tortoise_orm, location,
+    ctx: Context, tortoise_orm, location,
 ):
     config_file = ctx.obj["config_file"]
     name = ctx.obj["name"]
diff --git a/aerich/migrate.py b/aerich/migrate.py
index d859e02..862e8a2 100644
--- a/aerich/migrate.py
+++ b/aerich/migrate.py
@@ -111,10 +111,9 @@ async def migrate(cls, name) -> str:
         apps = Tortoise.apps
         diff_models = apps.get(cls.diff_app)
         app_models = apps.get(cls.app)
-        app_models.pop(cls._aerich, None)
 
-        cls._diff_models(diff_models, app_models)
-        cls._diff_models(app_models, diff_models, False)
+        cls.diff_models(diff_models, app_models)
+        cls.diff_models(app_models, diff_models, False)
 
         cls._merge_operators()
 
@@ -198,7 +197,7 @@ def write_old_models(cls, config: dict, app: str, location: str):
         cls.cp_models(app, old_model_files, os.path.join(location, app, cls.get_old_model_file()))
 
     @classmethod
-    def _diff_models(
+    def diff_models(
         cls, old_models: Dict[str, Type[Model]], new_models: Dict[str, Type[Model]], upgrade=True
     ):
         """
@@ -208,6 +207,9 @@ def _diff_models(
         :param upgrade:
         :return:
         """
+        old_models.pop(cls._aerich, None)
+        new_models.pop(cls._aerich, None)
+
         for new_model_str, new_model in new_models.items():
             if new_model_str not in old_models.keys():
                 cls._add_operator(cls.add_model(new_model), upgrade)
diff --git a/conftest.py b/conftest.py
index 668b162..4c2fa5e 100644
--- a/conftest.py
+++ b/conftest.py
@@ -1,11 +1,61 @@
+import asyncio
 import os
 
 import pytest
-from tortoise.contrib.test import finalizer, initializer
+from tortoise import Tortoise, expand_db_url, generate_schema_for_client
+from tortoise.backends.asyncpg.schema_generator import AsyncpgSchemaGenerator
+from tortoise.backends.mysql.schema_generator import MySQLSchemaGenerator
+from tortoise.backends.sqlite.schema_generator import SqliteSchemaGenerator
 
+from aerich.ddl.mysql import MysqlDDL
+from aerich.ddl.postgres import PostgresDDL
+from aerich.ddl.sqlite import SqliteDDL
+from aerich.migrate import Migrate
 
-@pytest.fixture(scope="module", autouse=True)
-def initialize_tests(request):
-    db_url = os.getenv("TEST_DB", "sqlite://:memory:")
-    initializer(["tests.models"], db_url=db_url)
-    request.addfinalizer(finalizer)
+db_url = os.getenv("TEST_DB", "sqlite://:memory:")
+tortoise_orm = {
+    "connections": {"default": expand_db_url(db_url, True)},
+    "apps": {
+        "models": {
+            "models": ["tests.models", "aerich.models"],
+            "default_connection": "default",
+        },
+    },
+}
+
+
+@pytest.fixture(scope="function", autouse=True)
+def reset_migrate():
+    Migrate.upgrade_operators = []
+    Migrate.downgrade_operators = []
+    Migrate._upgrade_fk_m2m_index_operators = []
+    Migrate._downgrade_fk_m2m_index_operators = []
+    Migrate._upgrade_m2m = []
+    Migrate._downgrade_m2m = []
+
+
+@pytest.fixture(scope="session")
+def loop():
+    loop = asyncio.get_event_loop()
+    return loop
+
+
+@pytest.fixture(scope="session", autouse=True)
+def initialize_tests(loop, request):
+    tortoise_orm['connections']['diff_models'] = "sqlite://:memory:"
+    tortoise_orm['apps']['diff_models'] = {"models": ["tests.diff_models"], "default_connection": "diff_models"}
+
+    loop.run_until_complete(Tortoise.init(config=tortoise_orm, _create_db=True))
+    loop.run_until_complete(
+        generate_schema_for_client(Tortoise.get_connection("default"), safe=True)
+    )
+
+    client = Tortoise.get_connection("default")
+    if client.schema_generator is MySQLSchemaGenerator:
+        Migrate.ddl = MysqlDDL(client)
+    elif client.schema_generator is SqliteSchemaGenerator:
+        Migrate.ddl = SqliteDDL(client)
+    elif client.schema_generator is AsyncpgSchemaGenerator:
+        Migrate.ddl = PostgresDDL(client)
+
+    request.addfinalizer(lambda: loop.run_until_complete(Tortoise._drop_databases()))
diff --git a/poetry.lock b/poetry.lock
index 06b86f1..6e024d8 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -90,14 +90,6 @@ dev = ["Cython (0.29.14)", "pytest (>=3.6.0)", "Sphinx (>=1.7.3,<1.8.0)", "sphin
 docs = ["Sphinx (>=1.7.3,<1.8.0)", "sphinxcontrib-asyncio (>=0.2.0,<0.3.0)", "sphinx-rtd-theme (>=0.2.4,<0.3.0)"]
 test = ["pycodestyle (>=2.5.0,<2.6.0)", "flake8 (>=3.7.9,<3.8.0)", "uvloop (>=0.14.0,<0.15.0)"]
 
-[[package]]
-category = "dev"
-description = "Enhance the standard unittest package with features for testing asyncio libraries"
-name = "asynctest"
-optional = false
-python-versions = ">=3.5"
-version = "0.13.0"
-
 [[package]]
 category = "dev"
 description = "Atomic file writes."
@@ -217,7 +209,7 @@ description = "the modular source code checker: pep8 pyflakes and co"
 name = "flake8"
 optional = false
 python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,>=2.7"
-version = "3.8.1"
+version = "3.8.2"
 
 [package.dependencies]
 mccabe = ">=0.6.0,<0.7.0"
@@ -412,6 +404,20 @@ wcwidth = "*"
 checkqa-mypy = ["mypy (v0.761)"]
 testing = ["argcomplete", "hypothesis (>=3.56)", "mock", "nose", "requests", "xmlschema"]
 
+[[package]]
+category = "dev"
+description = "Pytest support for asyncio."
+name = "pytest-asyncio"
+optional = false
+python-versions = ">= 3.5"
+version = "0.12.0"
+
+[package.dependencies]
+pytest = ">=5.4.0"
+
+[package.extras]
+testing = ["async_generator (>=1.3)", "coverage", "hypothesis (>=5.7.1)"]
+
 [[package]]
 category = "dev"
 description = "run tests in isolated forked subprocesses"
@@ -454,7 +460,7 @@ description = "Python 2 and 3 compatibility utilities"
 name = "six"
 optional = false
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*"
-version = "1.14.0"
+version = "1.15.0"
 
 [[package]]
 category = "main"
@@ -489,7 +495,7 @@ description = "Easy async ORM for python, built with relations in mind"
 name = "tortoise-orm"
 optional = false
 python-versions = "*"
-version = "0.16.11"
+version = "0.16.12"
 
 [package.dependencies]
 aiosqlite = ">=0.11.0"
@@ -498,10 +504,6 @@ iso8601 = ">=0.1.12"
 pypika = ">=0.36.5"
 typing-extensions = ">=3.7"
 
-[package.source]
-reference = "1f67b7a0ca1384365d6ff89d9e245e733166d1a6"
-type = "git"
-url = "https://github.com/long2ice/tortoise-orm.git"
 [[package]]
 category = "dev"
 description = "a fork of Python 2 and 3 ast modules with type comment support"
@@ -527,7 +529,7 @@ python-versions = "*"
 version = "0.1.9"
 
 [metadata]
-content-hash = "58a032bbb47859e87d2bce036af24149060cc531ff9220a14f6cd48db6252f39"
+content-hash = "35274e9622d359af475f573760ba687b31756b1b1de70bc4d75dab5ddbc5a93d"
 python-versions = "^3.8"
 
 [metadata.files]
@@ -581,10 +583,6 @@ asyncpg = [
     {file = "asyncpg-0.20.1-cp38-cp38-win_amd64.whl", hash = "sha256:2af6a5a705accd36e13292ea43d08c20b15e52d684beb522cb3a7d3c9c8f3f48"},
     {file = "asyncpg-0.20.1.tar.gz", hash = "sha256:394bf19bdddbba07a38cd6fb526ebf66e120444d6b3097332b78efd5b26495b0"},
 ]
-asynctest = [
-    {file = "asynctest-0.13.0-py3-none-any.whl", hash = "sha256:5da6118a7e6d6b54d83a8f7197769d046922a44d2a99c21382f0a6e4fadae676"},
-    {file = "asynctest-0.13.0.tar.gz", hash = "sha256:c27862842d15d83e6a34eb0b2866c323880eb3a75e4485b079ea11748fd77fac"},
-]
 atomicwrites = [
     {file = "atomicwrites-1.4.0-py2.py3-none-any.whl", hash = "sha256:6d1784dea7c0c8d4a5172b6c620f40b6e4cbfdf96d783691f2e1302a7b88e197"},
     {file = "atomicwrites-1.4.0.tar.gz", hash = "sha256:ae70396ad1a434f9c7046fd2dd196fc04b12f9e91ffb859164193be8b6168a7a"},
@@ -664,8 +662,8 @@ execnet = [
     {file = "execnet-1.7.1.tar.gz", hash = "sha256:cacb9df31c9680ec5f95553976c4da484d407e85e41c83cb812aa014f0eddc50"},
 ]
 flake8 = [
-    {file = "flake8-3.8.1-py2.py3-none-any.whl", hash = "sha256:6c1193b0c3f853ef763969238f6c81e9e63ace9d024518edc020d5f1d6d93195"},
-    {file = "flake8-3.8.1.tar.gz", hash = "sha256:ea6623797bf9a52f4c9577d780da0bb17d65f870213f7b5bcc9fca82540c31d5"},
+    {file = "flake8-3.8.2-py2.py3-none-any.whl", hash = "sha256:ccaa799ef9893cebe69fdfefed76865aeaefbb94cb8545617b2298786a4de9a5"},
+    {file = "flake8-3.8.2.tar.gz", hash = "sha256:c69ac1668e434d37a2d2880b3ca9aafd54b3a10a3ac1ab101d22f29e29cf8634"},
 ]
 iso8601 = [
     {file = "iso8601-0.1.12-py2.py3-none-any.whl", hash = "sha256:210e0134677cc0d02f6028087fee1df1e1d76d372ee1db0bf30bf66c5c1c89a3"},
@@ -766,6 +764,9 @@ pytest = [
     {file = "pytest-5.4.2-py3-none-any.whl", hash = "sha256:95c710d0a72d91c13fae35dce195633c929c3792f54125919847fdcdf7caa0d3"},
     {file = "pytest-5.4.2.tar.gz", hash = "sha256:eb2b5e935f6a019317e455b6da83dd8650ac9ffd2ee73a7b657a30873d67a698"},
 ]
+pytest-asyncio = [
+    {file = "pytest-asyncio-0.12.0.tar.gz", hash = "sha256:475bd2f3dc0bc11d2463656b3cbaafdbec5a47b47508ea0b329ee693040eebd2"},
+]
 pytest-forked = [
     {file = "pytest-forked-1.1.3.tar.gz", hash = "sha256:1805699ed9c9e60cb7a8179b8d4fa2b8898098e82d229b0825d8095f0f261100"},
     {file = "pytest_forked-1.1.3-py2.py3-none-any.whl", hash = "sha256:1ae25dba8ee2e56fb47311c9638f9e58552691da87e82d25b0ce0e4bf52b7d87"},
@@ -798,8 +799,8 @@ regex = [
     {file = "regex-2020.5.14.tar.gz", hash = "sha256:ce450ffbfec93821ab1fea94779a8440e10cf63819be6e176eb1973a6017aff5"},
 ]
 six = [
-    {file = "six-1.14.0-py2.py3-none-any.whl", hash = "sha256:8f3cd2e254d8f793e7f3d6d9df77b92252b52637291d0f0da013c76ea2724b6c"},
-    {file = "six-1.14.0.tar.gz", hash = "sha256:236bdbdce46e6e6a3d61a337c0f8b763ca1e8717c03b369e87a7ec7ce1319c0a"},
+    {file = "six-1.15.0-py2.py3-none-any.whl", hash = "sha256:8b74bedcbbbaca38ff6d7491d76f2b06b3592611af620f8426e82dddb04a5ced"},
+    {file = "six-1.15.0.tar.gz", hash = "sha256:30639c035cdb23534cd4aa2dd52c3bf48f06e5f4a941509c8bafd8ce11080259"},
 ]
 sniffio = [
     {file = "sniffio-1.1.0-py3-none-any.whl", hash = "sha256:20ed6d5b46f8ae136d00b9dcb807615d83ed82ceea6b2058cecb696765246da5"},
@@ -813,7 +814,9 @@ toml = [
     {file = "toml-0.10.1-py2.py3-none-any.whl", hash = "sha256:bda89d5935c2eac546d648028b9901107a595863cb36bae0c73ac804a9b4ce88"},
     {file = "toml-0.10.1.tar.gz", hash = "sha256:926b612be1e5ce0634a2ca03470f95169cf16f939018233a670519cb4ac58b0f"},
 ]
-tortoise-orm = []
+tortoise-orm = [
+    {file = "tortoise-orm-0.16.12.tar.gz", hash = "sha256:170e4bbfe1c98223ad1fba33d7fded7923e4bb49c9d74c78bd173a0ebc861658"},
+]
 typed-ast = [
     {file = "typed_ast-1.4.1-cp35-cp35m-manylinux1_i686.whl", hash = "sha256:73d785a950fc82dd2a25897d525d003f6378d1cb23ab305578394694202a58c3"},
     {file = "typed_ast-1.4.1-cp35-cp35m-manylinux1_x86_64.whl", hash = "sha256:aaee9905aee35ba5905cfb3c62f3e83b3bec7b39413f0a7f19be4e547ea01ebb"},
diff --git a/pyproject.toml b/pyproject.toml
index 5ed2468..b6e2fd0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -6,13 +6,12 @@ authors = ["long2ice <long2ice@gmail.com>"]
 
 [tool.poetry.dependencies]
 python = "^3.8"
-tortoise-orm = {git = "https://github.com/tortoise-orm/tortoise-orm.git", branch = "develop"}
+tortoise-orm = "*"
 asyncclick = "*"
 pydantic = "*"
 
 [tool.poetry.dev-dependencies]
 taskipy = "*"
-asynctest = "*"
 flake8 = "*"
 isort = "*"
 black = "^19.10b0"
@@ -21,6 +20,7 @@ aiomysql = "*"
 asyncpg = "*"
 pytest-xdist = "*"
 mypy = "*"
+pytest-asyncio = "*"
 
 [tool.taskipy.tasks]
 export = "poetry export -f requirements.txt --without-hashes > requirements.txt"
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 4633e09..a2baa92 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -6,7 +6,6 @@ appdirs==1.4.4
 async-generator==1.10
 asyncclick==7.0.9
 asyncpg==0.20.1
-asynctest==0.13.0
 atomicwrites==1.4.0; sys_platform == "win32"
 attrs==19.3.0
 black==19.10b0
@@ -16,7 +15,7 @@ click==7.1.2
 colorama==0.4.3; sys_platform == "win32"
 cryptography==2.9.2
 execnet==1.7.1
-flake8==3.8.1
+flake8==3.8.2
 iso8601==0.1.12; sys_platform == "win32" or implementation_name != "cpython"
 isort==4.3.21
 mccabe==0.6.1
@@ -35,14 +34,15 @@ pymysql==0.9.2
 pyparsing==2.4.7
 pypika==0.37.6
 pytest==5.4.2
+pytest-asyncio==0.12.0
 pytest-forked==1.1.3
 pytest-xdist==1.32.0
 regex==2020.5.14
-six==1.14.0
+six==1.15.0
 sniffio==1.1.0
 taskipy==1.2.1
 toml==0.10.1
--e git+https://github.com/long2ice/tortoise-orm.git@1f67b7a0ca1384365d6ff89d9e245e733166d1a6#egg=tortoise-orm
+tortoise-orm==0.16.12
 typed-ast==1.4.1
 typing-extensions==3.7.4.2
 wcwidth==0.1.9
diff --git a/requirements.txt b/requirements.txt
index 623ebe3..863509f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,4 +7,5 @@ iso8601==0.1.12; sys_platform == "win32" or implementation_name != "cpython"
 pydantic==1.5.1
 pypika==0.37.6
 sniffio==1.1.0
+tortoise-orm==0.16.12
 typing-extensions==3.7.4.2
diff --git a/tests/__init__.py b/tests/__init__.py
index 4abc103..e69de29 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1,6 +0,0 @@
-TORTOISE_ORM = {
-    "connections": {"default": "mysql://root:123456@127.0.0.1:3306/test"},
-    "apps": {
-        "models": {"models": ["tests.models", "aerich.models"], "default_connection": "default"}
-    },
-}
diff --git a/tests/diff_models.py b/tests/diff_models.py
new file mode 100644
index 0000000..7f5af93
--- /dev/null
+++ b/tests/diff_models.py
@@ -0,0 +1,56 @@
+import datetime
+from enum import IntEnum
+
+from tortoise import Model, fields
+
+
+class ProductType(IntEnum):
+    article = 1
+    page = 2
+
+
+class PermissionAction(IntEnum):
+    create = 1
+    delete = 2
+    update = 3
+    read = 4
+
+
+class Status(IntEnum):
+    on = 1
+    off = 0
+
+
+class User(Model):
+    username = fields.CharField(max_length=20,)
+    password = fields.CharField(max_length=200)
+    last_login = fields.DatetimeField(description="Last Login", default=datetime.datetime.now)
+    is_active = fields.BooleanField(default=True, description="Is Active")
+    is_superuser = fields.BooleanField(default=False, description="Is SuperUser")
+    avatar = fields.CharField(max_length=200, default="")
+    intro = fields.TextField(default="")
+
+
+class Category(Model):
+    slug = fields.CharField(max_length=200)
+    user = fields.ForeignKeyField("diff_models.User", description="User")
+    created_at = fields.DatetimeField(auto_now_add=True)
+
+
+class Product(Model):
+    categories = fields.ManyToManyField("diff_models.Category")
+    name = fields.CharField(max_length=50)
+    view_num = fields.IntField(description="View Num")
+    sort = fields.IntField()
+    is_reviewed = fields.BooleanField(description="Is Reviewed")
+    type = fields.IntEnumField(ProductType, description="Product Type")
+    image = fields.CharField(max_length=200)
+    body = fields.TextField()
+    created_at = fields.DatetimeField(auto_now_add=True)
+
+
+class Config(Model):
+    label = fields.CharField(max_length=200)
+    key = fields.CharField(max_length=20)
+    value = fields.JSONField()
+    status: Status = fields.IntEnumField(Status, default=Status.on)
diff --git a/tests/test_ddl.py b/tests/test_ddl.py
index 0ed2897..5ab4040 100644
--- a/tests/test_ddl.py
+++ b/tests/test_ddl.py
@@ -1,114 +1,101 @@
-from tortoise import Tortoise
-from tortoise.backends.asyncpg.schema_generator import AsyncpgSchemaGenerator
-from tortoise.backends.mysql.schema_generator import MySQLSchemaGenerator
-from tortoise.backends.sqlite.schema_generator import SqliteSchemaGenerator
-from tortoise.contrib import test
-
 from aerich.ddl.mysql import MysqlDDL
 from aerich.ddl.postgres import PostgresDDL
 from aerich.ddl.sqlite import SqliteDDL
+from aerich.migrate import Migrate
 from tests.models import Category
 
 
-class TestDDL(test.TruncationTestCase):
-    maxDiff = None
-
-    def setUp(self) -> None:
-        client = Tortoise.get_connection("models")
-        if client.schema_generator is MySQLSchemaGenerator:
-            self.ddl = MysqlDDL(client)
-        elif client.schema_generator is SqliteSchemaGenerator:
-            self.ddl = SqliteDDL(client)
-        elif client.schema_generator is AsyncpgSchemaGenerator:
-            self.ddl = PostgresDDL(client)
-
-    def test_create_table(self):
-        ret = self.ddl.create_table(Category)
-        if isinstance(self.ddl, MysqlDDL):
-            self.assertEqual(
-                ret,
-                """CREATE TABLE IF NOT EXISTS `category` (
+def test_create_table():
+    ret = Migrate.ddl.create_table(Category)
+    if isinstance(Migrate.ddl, MysqlDDL):
+        assert (
+            ret
+            == """CREATE TABLE IF NOT EXISTS `category` (
     `id` INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
     `slug` VARCHAR(200) NOT NULL,
     `name` VARCHAR(200) NOT NULL,
     `created_at` DATETIME(6) NOT NULL  DEFAULT CURRENT_TIMESTAMP(6),
     `user_id` INT NOT NULL COMMENT 'User',
     CONSTRAINT `fk_category_user_e2e3874c` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE
-) CHARACTER SET utf8mb4;""",
-            )
-        elif isinstance(self.ddl, SqliteDDL):
-            self.assertEqual(
-                ret,
-                """CREATE TABLE IF NOT EXISTS "category" (
+) CHARACTER SET utf8mb4;"""
+        )
+
+    elif isinstance(Migrate.ddl, SqliteDDL):
+        assert (
+            ret
+            == """CREATE TABLE IF NOT EXISTS "category" (
     "id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
     "slug" VARCHAR(200) NOT NULL,
     "name" VARCHAR(200) NOT NULL,
     "created_at" TIMESTAMP NOT NULL  DEFAULT CURRENT_TIMESTAMP,
     "user_id" INT NOT NULL REFERENCES "user" ("id") ON DELETE CASCADE /* User */
-);""",
-            )
-        elif isinstance(self.ddl, PostgresDDL):
-            self.assertEqual(
-                ret,
-                """CREATE TABLE IF NOT EXISTS "category" (
+);"""
+        )
+
+    elif isinstance(Migrate.ddl, PostgresDDL):
+        assert (
+            ret
+            == """CREATE TABLE IF NOT EXISTS "category" (
     "id" SERIAL NOT NULL PRIMARY KEY,
     "slug" VARCHAR(200) NOT NULL,
     "name" VARCHAR(200) NOT NULL,
     "created_at" TIMESTAMP NOT NULL  DEFAULT CURRENT_TIMESTAMP,
     "user_id" INT NOT NULL REFERENCES "user" ("id") ON DELETE CASCADE
 );
-COMMENT ON COLUMN "category"."user_id" IS 'User';""",
-            )
-
-    def test_drop_table(self):
-        ret = self.ddl.drop_table(Category)
-        self.assertEqual(ret, "DROP TABLE IF EXISTS category")
-
-    def test_add_column(self):
-        ret = self.ddl.add_column(Category, Category._meta.fields_map.get("name"))
-        if isinstance(self.ddl, MysqlDDL):
-            self.assertEqual(ret, "ALTER TABLE category ADD `name` VARCHAR(200) NOT NULL")
-        elif isinstance(self.ddl, PostgresDDL):
-            self.assertEqual(ret, 'ALTER TABLE category ADD "name" VARCHAR(200) NOT NULL')
-        elif isinstance(self.ddl, SqliteDDL):
-            self.assertEqual(ret, 'ALTER TABLE category ADD "name" VARCHAR(200) NOT NULL')
-
-    def test_drop_column(self):
-        ret = self.ddl.drop_column(Category, "name")
-        self.assertEqual(ret, "ALTER TABLE category DROP COLUMN name")
-        self.assertEqual(ret, "ALTER TABLE category DROP COLUMN name")
-
-    def test_add_index(self):
-        index = self.ddl.add_index(Category, ["name"])
-        index_u = self.ddl.add_index(Category, ["name"], True)
-        if isinstance(self.ddl, MysqlDDL):
-            self.assertEqual(
-                index, "ALTER TABLE category ADD  INDEX idx_category_name_8b0cb9 (`name`)"
-            )
-            self.assertEqual(
-                index_u, "ALTER TABLE category ADD UNIQUE INDEX uid_category_name_8b0cb9 (`name`)"
-            )
-        elif isinstance(self.ddl, SqliteDDL):
-            self.assertEqual(
-                index_u, 'ALTER TABLE category ADD UNIQUE INDEX uid_category_name_8b0cb9 ("name")'
-            )
-            self.assertEqual(
-                index_u, 'ALTER TABLE category ADD UNIQUE INDEX uid_category_name_8b0cb9 ("name")'
-            )
-
-    def test_drop_index(self):
-        ret = self.ddl.drop_index(Category, ["name"])
-        self.assertEqual(ret, "ALTER TABLE category DROP INDEX idx_category_name_8b0cb9")
-        ret = self.ddl.drop_index(Category, ["name"], True)
-        self.assertEqual(ret, "ALTER TABLE category DROP INDEX uid_category_name_8b0cb9")
-
-    def test_add_fk(self):
-        ret = self.ddl.add_fk(Category, Category._meta.fields_map.get("user"))
-        self.assertEqual(
-            ret,
-            "ALTER TABLE category ADD CONSTRAINT `fk_category_user_e2e3874c` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE",
+COMMENT ON COLUMN "category"."user_id" IS 'User';"""
         )
 
-    def test_drop_fk(self):
-        ret = self.ddl.drop_fk(Category, Category._meta.fields_map.get("user"))
-        self.assertEqual(ret, "ALTER TABLE category DROP FOREIGN KEY fk_category_user_e2e3874c")
+
+def test_drop_table():
+    ret = Migrate.ddl.drop_table(Category)
+    assert ret == "DROP TABLE IF EXISTS category"
+
+
+def test_add_column():
+    ret = Migrate.ddl.add_column(Category, Category._meta.fields_map.get("name"))
+    if isinstance(Migrate.ddl, MysqlDDL):
+        assert ret == "ALTER TABLE category ADD `name` VARCHAR(200) NOT NULL"
+    elif isinstance(Migrate.ddl, PostgresDDL):
+        assert ret == 'ALTER TABLE category ADD "name" VARCHAR(200) NOT NULL'
+    elif isinstance(Migrate.ddl, SqliteDDL):
+        assert ret == 'ALTER TABLE category ADD "name" VARCHAR(200) NOT NULL'
+
+
+def test_drop_column():
+    ret = Migrate.ddl.drop_column(Category, "name")
+    assert ret == "ALTER TABLE category DROP COLUMN name"
+    assert ret == "ALTER TABLE category DROP COLUMN name"
+
+
+def test_add_index():
+    index = Migrate.ddl.add_index(Category, ["name"])
+    index_u = Migrate.ddl.add_index(Category, ["name"], True)
+    if isinstance(Migrate.ddl, MysqlDDL):
+        assert index == "ALTER TABLE category ADD  INDEX idx_category_name_8b0cb9 (`name`)"
+
+        assert index_u == "ALTER TABLE category ADD UNIQUE INDEX uid_category_name_8b0cb9 (`name`)"
+
+    elif isinstance(Migrate.ddl, SqliteDDL):
+        assert index_u == 'ALTER TABLE category ADD UNIQUE INDEX uid_category_name_8b0cb9 ("name")'
+
+        assert index_u == 'ALTER TABLE category ADD UNIQUE INDEX uid_category_name_8b0cb9 ("name")'
+
+
+def test_drop_index():
+    ret = Migrate.ddl.drop_index(Category, ["name"])
+    assert ret == "ALTER TABLE category DROP INDEX idx_category_name_8b0cb9"
+    ret = Migrate.ddl.drop_index(Category, ["name"], True)
+    assert ret == "ALTER TABLE category DROP INDEX uid_category_name_8b0cb9"
+
+
+def test_add_fk():
+    ret = Migrate.ddl.add_fk(Category, Category._meta.fields_map.get("user"))
+    assert (
+        ret
+        == "ALTER TABLE category ADD CONSTRAINT `fk_category_user_e2e3874c` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE CASCADE"
+    )
+
+
+def test_drop_fk():
+    ret = Migrate.ddl.drop_fk(Category, Category._meta.fields_map.get("user"))
+    assert ret == "ALTER TABLE category DROP FOREIGN KEY fk_category_user_e2e3874c"
diff --git a/tests/test_migrate.py b/tests/test_migrate.py
new file mode 100644
index 0000000..55baaea
--- /dev/null
+++ b/tests/test_migrate.py
@@ -0,0 +1,41 @@
+from tortoise import Tortoise
+
+from aerich.ddl.mysql import MysqlDDL
+from aerich.ddl.postgres import PostgresDDL
+from aerich.ddl.sqlite import SqliteDDL
+from aerich.migrate import Migrate
+
+
+def test_migrate():
+    apps = Tortoise.apps
+    models = apps.get("models")
+    diff_models = apps.get("diff_models")
+    Migrate.diff_models(diff_models, models)
+    Migrate.diff_models(models, diff_models, False)
+    if isinstance(Migrate.ddl, MysqlDDL):
+        assert Migrate.upgrade_operators == [
+            "ALTER TABLE category ADD `name` VARCHAR(200) NOT NULL",
+            "ALTER TABLE user ADD UNIQUE INDEX uid_user_usernam_9987ab (`username`)",
+        ]
+        assert Migrate.downgrade_operators == [
+            "ALTER TABLE category DROP COLUMN name",
+            "ALTER TABLE user DROP INDEX uid_user_usernam_9987ab",
+        ]
+    elif isinstance(Migrate.ddl, SqliteDDL):
+        assert Migrate.upgrade_operators == [
+            'ALTER TABLE category ADD "name" VARCHAR(200) NOT NULL',
+            'ALTER TABLE user ADD UNIQUE INDEX uid_user_usernam_9987ab ("username")',
+        ]
+        assert Migrate.downgrade_operators == [
+            "ALTER TABLE category DROP COLUMN name",
+            "ALTER TABLE user DROP INDEX uid_user_usernam_9987ab",
+        ]
+    elif isinstance(Migrate.ddl, PostgresDDL):
+        assert Migrate.upgrade_operators == [
+            'ALTER TABLE category ADD "name" VARCHAR(200) NOT NULL',
+            'ALTER TABLE user ADD UNIQUE INDEX uid_user_usernam_9987ab ("username")',
+        ]
+        assert Migrate.downgrade_operators == [
+            "ALTER TABLE category DROP COLUMN name",
+            "ALTER TABLE user DROP INDEX uid_user_usernam_9987ab",
+        ]