doc/development/testing_guide/best_practices.md
# Testing best practices
## Test speed
It's important that we make an effort to write tests that are accurate
and effective _as well as_ fast.
Here are some things to keep in mind regarding test performance:
- `double` and `spy` are faster than `FactoryBot.build(...)`
- `FactoryBot.build(...)` and `.build_stubbed` are faster than `.create`.
- Don't `create` an object when `build`, `build_stubbed`, `attributes_for`,
`spy`, or `double` will do. Database persistence is slow!
- Don't mark a feature as requiring JavaScript (through `:js` in RSpec) unless it's _actually_ required for the test to be valid. Headless browser testing is slow!
### Table-based / Parameterized tests
This style of testing is used to exercise one piece of code with a comprehensive
range of inputs. By specifying the test case once, alongside a table of inputs
and the expected output for each, your tests can be made easier to read and more
compact.
We use the [rspec-parameterized](https://github.com/tomykaira/rspec-parameterized)
gem. A short example, using the table syntax and checking Ruby equality for a
range of inputs, might look like this:
```ruby
describe "#==" do
using RSpec::Parameterized::TableSyntax
let(:project1) { create(:project) }
let(:project2) { create(:project) }
where(:a, :b, :result) do
1 | 1 | true
1 | 2 | false
true | true | true
true | false | false
project1 | project1 | true
project2 | project2 | true
project 1 | project2 | false
end
with_them do
it { expect(a == b).to eq(result) }
it 'is isomorphic' do
expect(b == a).to eq(result)
end
end
end
```
### Time-sensitive tests
[Timecop](https://github.com/travisjeffery/timecop) is available in our
Ruby-based tests for verifying things that are time-sensitive. Any test that
exercises or verifies something time-sensitive should make use of Timecop to
prevent transient test failures.
Example:
```ruby
it 'is overdue' do
issue = build(:issue, due_date: Date.tomorrow)
Timecop.freeze(3.days.from_now) do
expect(issue).to be_overdue
end
end
```