I figured it out. First, some details. I am using Codeception v2.4.1, powered by PHPUnit 7.1.4. The answer is:
in codeception.yml, add these two lines:
Here _bootstrap.php can be whatever you want the name of your bootstrap file to be.
You must place _bootstrap.php in each of the following directories as follows:
In my tests/unit/_bootstrap.php file, I placed the following code:
Autoload::addNamespace('myclassnamespace', __DIR__ . '/../../Classes/');
To make sure I had the right path to Classes, I used trigger_error(DIR) in my _bootstrap.php before i added the Autoload line.
Then in my tests/unit/TestAddCest.php, I placed the following line at the beginning of the file:
And in my test function looks like this (note the instantiation of the User class):
public function tryToTest(UnitTester $I)
$user = new mynamespace\User('someusername');
I hand typed that function because I'm not on the same machine with the code and didn't feel like getting it over, so it may have a typo or bug, but you get the idea.