snqb TDD Discipline
Write the test. Watch it fail. Write minimal code. Watch it pass. Repeat.
The Cycle
RED → GREEN → REFACTOR → commit
- RED: Write one test. Run it. Watch it FAIL (not error—fail because feature is missing).
- GREEN: Write simplest code to pass. Just enough. No more.
- REFACTOR: Clean up while tests green. Then commit.
Rules
- No production code without a failing test first
- Wrote code before the test? Delete it. Start over.
- If you didn't watch the test fail, you don't know if it tests the right thing.
When to Skip
- Throwaway prototypes (that you'll actually throw away)
- Generated code
- Config files
Thinking "skip TDD just this once"? That's rationalization. Stop.
Anti-Patterns
| Don't | Do |
|---|---|
| Test mocks instead of real code | Test real code |
test_retry_works |
retries_failed_operations_3_times |
| Multiple behaviors in one test | One behavior per test |
| Keep "reference code" after deleting untested code | Delete all untested code |
Examples
Good Test Name
def test_transfer_fails_when_insufficient_balance():
...
Bad Test Name
def test_transfer(): # What about transfer?
...
Minimal Green
# RED: test expects add(2, 3) == 5
# GREEN (wrong - too much):
def add(a, b):
if not isinstance(a, (int, float)):
raise TypeError("...")
return a + b
# GREEN (right - just enough):
def add(a, b):
return a + b