What is the argument against using before, let and subject in RSpec tests? [closed]

Answer 1

My thoughts...

1. By using context, before, let, let! Test suit performs better (run faster)
2. By using this constructs one can create shared contexts using same idea of inheritance, so one can override what's needed on specific situations
3. The powerful shoulda matchers relies on subject in order to work
4. The rails specific type of specs (controller, model) relies on let, before and context behind the scene
5. Let is lazy load, it does not represent oversharing if is never referenced within specific tests, meaning that even if an it has access to 100 lets, but it only uses 1, the other 99 never gets computed at all
6. Is not only the test code what a developer have to read to understand the test suit, is also the output of the test suit when running, it gives a lot of sense to what is being tested
7. I agree on before(:all) obfuscates a lot of dependencies, but for performance reason I will use it if needed

Answer 2

Avoid its, let, let!, specify, before, and subject.

Really? That cuts out the legs out from under the RSpec DSL. Might as well go back to using test/unit.

As to why they avoid let, Thoughtbot says: "We have a blog post coming out before too long that will hopefully explain." I'll wait with interest for those pearls of wisdom -- but in the meantime, take the style guide with a grain of salt.

EDIT

The aforementioned blog post makes for some interesting reading.

Answer 3

Interesting question; something that I want to know more about as well.... So dug in a bit, and here is what I uncovered:

Thoughtbot style guide dictum about let, etc.

1. In an earlier version of the style guide, there's more to that statement:

   Avoid its, let, let!, specify, subject, and other DSLs. Prefer explicitness and consistency.

2. ThoughtBot folks made a post on let name let's not. See also the link to the Github Commit Comment conversation

3. On one of their recent podcasts Joe Ferris, the CTO of ThoughtBot, explains why it's not a good idea to use let and subject. Check out the podcast titled Something Else Was Smellier from the 27m37s mark onwards for the next 5 minutes.

4. Testing Anti-pattern 'Mystery Guest' which is dealt with in detail in an older ThoughtBot blogpost is the main reason for why not to use let and its cousins.

To summarize my understanding of all the above very succinctly:

Using let et al makes it difficult to understand what's happening within the test on a quick glance, and requires the person to spend some time in making the connections.

Write tests such that it is easy to understand without much effort.

In addition, using let liberally in tests results in over-sharing among the tests, as well as makes implicit common fixtures - i.e. having a common fixture to start with for every test being written even when it does not apply.

before(:all)

The argument against using before(:all) is straight-forward. As explained in the old rspec documentation:

Warning: The use of before(:all) and after(:all) is generally discouraged because it introduces dependencies between the Examples. Still, it might prove useful for very expensive operations if you know what you are doing.

before(:all) gets executed only once at the start of the ExampleGroup. As such there is a potential to inadvertently introduce dependencies between the Examples. Thoughtbot's assertion about the tests not being easy to understand applies to this as well.

In conclusion, the advise for writing better specs seems to be:

1. Write tests such that they are easy to understand on a quick glance.
2. Know what you are doing.