DRY, string, and unit testing
- by Rodrigue
I have a recurring question when writing unit tests for code that involves constant string values.
Let's take an example of a method/function that does some processing and returns a string containing a pre-defined constant. In python, that would be something like:
STRING_TEMPLATE = "/some/constant/string/with/%s/that/needs/interpolation/"
def process(some_param):
# We do some meaningful work that gives us a value
result = _some_meaningful_action()
return STRING_TEMPLATE % result
If I want to unit test process, one of my tests will check the return value. This is where I wonder what the best solution is.
In my unit test, I can:
apply DRY and use the already defined constant
repeat myself and rewrite the entire string
def test_foo_should_return_correct_url():
string_result = process()
# Applying DRY and using the already defined constant
assert STRING_TEMPLATE % "1234" == string_result
# Repeating myself, repeating myself
assert "/some/constant/string/with/1234/that/needs/interpolation/" == url
The advantage I see in the former is that my test will break if I put the wrong string value in my constant. The inconvenient is that I may be rewriting the same string over and over again across different unit tests.
