Don’t repeat the logic in the unit tests

There are multiple mistakes you can do, as software engineer, when you define and write the unit tests for your software.

One of the most common I saw it was to repeat the logic from the tested function/method in the unit test function

INTERMEDIATE_VALUES = [5, 6, 7, 8, 9, 10]


def my_func(x):
		return x + 1

	if x > HARD_UPPER:
		return x + x

	if x < SOFT_LOWER:
		return x ** x

Let’s imagine we want to test this dummy function, my_func and we would do it in this way:

from functions import my_func

def test_myfunc():
    test_values = [4, 7, 8, 10]
    for x in test_values:
        if x in [5, 6, 7, 8, 9, 10]:
            expected = x + 1
        if x > 10:
            expected = x + x
        if x < 5:
            expected = x ** x

        assert expected == my_func(x)

It looks nice. It tests the boundaries, it seems to test all the intervals. But, let’s imagine someone is going into and does this change, increases the SOFT_LOWER with 1 and removes 5 from INTERMEDIATE_VALUES.

INTERMEDIATE_VALUES = [6, 7, 8, 9, 10]

If we run our tests, everything is green, but some results are not the expected ones, for example, my_func(5), before 5 was in INTERMEDIATE_VALUES and the result was 6. Now, 5 is under the condition if x < 5 so, the result is 5 ^ 5 = 3125.

Ofcourse, abose it is just a silly example where I tried to copy/paste the logic from the target function to the test and the easier fix would be just to try to hardcode the boundaries and some itermediate values, like:

def test_myfunc():
    assert my_func(4) == 256
    assert my_func(5) == 6
    assert my_func(10) == 11
    assert my_func(11) == 22
    assert my_func(8) == 9

Now, we can see the test is failing for x=5

>       assert my_func(5) == 6
E       assert 3125 == 6
E        +  where 3125 = my_func(5)

This is the case when the border values really matters and we want to be sure the developer is councious of this change (they will see the tests failing). This such case can be for example the tax applied (we don’t want to change the VAT value for a country too often, right?) or the maximum number of connected devices (eg: Netflix).

If we can argue the values are not so sensitive we could import directly the constants and use them instead of hardcoding in the test (eg: the time when the weekely report email is sent to the team’s PM and someone change it by mistake from 5PM to 5AM).

Backup database in S3

A simple cron backup script of the databse in aws s3. Our script is called and it looks like this:

NOW=$(date +"%m_%d_%Y")
mysqldump --login-path=s3gallery --databases $DB | gzip > $BACKUPFILE
aws s3 cp $BACKUPFILE s3://$BACKUPFILE --profile backuper

And now a few explanations about the script.

First of all we need to have installed the awscli command.

Afterwords, as you can see, the database password is not hardcoded into the script. We can setup the password with mysql_config_editor. This will store authentication credentials in an encrypted login file named .mylogin.cnf.

For our example database, razvantudorica, and database user myuser, we can run

mysql_config_editor set --login-path=razvantudorica --host=localhost --user=myuser --password

The next step is to configure aws s3 bucket and credentials.

  • Create a bucket in s3, in our example is called
  • Create the IAM credentials and save them in ~/.aws/credentials as
  • And in ~/.aws/config add
[profile backuper]
  • The last step is to test our script. If no error occurs at running and the backup file is uploaded successfully in S3, then everything is correct and we can add it the crontab list.
  • Run crontab -e and add this line
0  1 * * * /root/ >> /var/log/mysqlbackup.log

Unknown database type enum requested

Using symfony (5) console command to create new migration based on my entities, I encountered this error.

php bin/console doctrine:migrations:diff

Unknown database type enum requested, Doctrine\DBAL\Platforms\MySQL57Platform may not support it.

The simplest solution is to add mapping_types in config\packages\doctrine.yml

        # ...
            enum: string

Upload asynchronously to Amazon S3 using Tornado

TornadoWeb is a great non-blocking web server written in Python and Boto3 is the Amazon Web Services (AWS) SDK for Python, which allows developers to write in a very easy manner software that makes use of Amazon services like S3. Unfortunately boto3 S3 wrapper is blocking and if you would just use it out of the box in a Tornado application it will block the main thread because it uses a synchronous HTTP client.
Continue reading Upload asynchronously to Amazon S3 using Tornado