Write tests that are readable, reliable, and fast. Follow these patterns consistently.
Arrange/Act/Assert
Every test has three sections separated by blank lines:
- Arrange — set up objects, database state, dependencies
- Act — exercise the system under test (one action)
- Assert — verify the result
it "adds the tag to the user" do
tag = create(:tag)
user = create(:user, tags: [])
user.add_tag(tag)
expect(user.tags).to eq([tag]) end
### Rules
- Separate each section with a blank line for visual clarity.
- Never mix expectations into the Arrange section. Use `allow` in Arrange, `expect(...).to have_received` in Assert.
- Prefer inline setup over `let`/`before` — all preconditions should be visible in each test body.
- If a test needs complex shared setup, that's a signal the implementation may need refactoring.
## Capybara Selectors
- **Always reach for semantic selectors first** (`:label`, `:button`, `:link`, `:field`). Only fall back to CSS selectors when no semantic selector exists.
- Locate elements by accessible names and descriptions, not CSS classes or IDs.
- Never use multiple separate `has_css?` calls with OR logic — combine with CSS comma syntax or use Capybara built-in selectors.
```ruby
# Bad — sequential timeout trap
page.has_css?("label[for='#{id}']", text: name) ||
page.has_css?("label:has(##{id})", text: name)
# Acceptable — combined CSS selector (use only when no semantic selector exists)
page.has_css?("label[for='#{id}'], label:has(##{id})", text: name)
# Default choice — semantic selector (always prefer this)
page.has_selector(:label, name, for: id)
Rule of thumb: If you're writing has_css? in a Capybara test, stop and check whether a semantic selector (:label, :button, :link, :field) can do the job. It almost always can.
Test Performance
- Tests that are slow compound over time. Be aware of test budget concepts.
- Flag tests with excessive setup as candidates for refactoring.
- Prefer unit tests over integration tests when the same logic can be verified faster.
- Don't stub the system under test — stub dependencies, not the thing you're testing.
References
For detailed examples and background, read:
references/arrange-act-assert.mdreferences/capybara-selectors.mdreferences/test-budget.md
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