tdd

Name: tdd
Author: stevesolun

560stars68forks

How to install tdd?

stevesolun/ctx/tdd

$npx -y skills add stevesolun/ctx --skill tdd

Installs into the current project.

Summary

Test-driven development with red-green-refactor loop. Use when user wants to build features or fix bugs using TDD, mentions "red-green-refactor", wants integration tests, or asks for test-first development.

Files · 1

View on GitHub

SKILL.md

1	# Test-Driven Development
2
3	## Philosophy
4
5	Core principle: Tests should verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't.
6
7	Good tests are integration-style: they exercise real code paths through public APIs. They describe _what_ the system does, not _how_ it does it. A good test reads like a specification - "user can checkout with valid cart" tells you exactly what capability exists. These tests survive refactors because they don't care about internal structure.
8
9	Bad tests are coupled to implementation. They mock internal collaborators, test private methods, or verify through external means (like querying a database directly instead of using the interface). The warning sign: your test breaks when you refactor, but behavior hasn't changed. If you rename an internal function and tests fail, those tests were testing implementation, not behavior.
10
11	See [tests.md](tests.md) for examples and [mocking.md](mocking.md) for mocking guidelines.
12
13	## Anti-Pattern: Horizontal Slices
14
15	DO NOT write all tests first, then all implementation. This is "horizontal slicing" - treating RED as "write all tests" and GREEN as "write all code."
16
17	This produces crap tests:
18
19	- Tests written in bulk test _imagined_ behavior, not _actual_ behavior
20	- You end up testing the _shape_ of things (data structures, function signatures) rather than user-facing behavior
21	- Tests become insensitive to real changes - they pass when behavior breaks, fail when behavior is fine
22	- You outrun your headlights, committing to test structure before understanding the implementation
23
24	Correct approach: Vertical slices via tracer bullets. One test → one implementation → repeat. Each test responds to what you learned from the previous cycle. Because you just wrote the code, you know exactly what behavior matters and how to verify it.
25
26	```
27	WRONG (horizontal):
28	RED: test1, test2, test3, test4, test5
29	GREEN: impl1, impl2, impl3, impl4, impl5
30
31	RIGHT (vertical):
32	RED→GREEN: test1→impl1
33	RED→GREEN: test2→impl2
34	RED→GREEN: test3→impl3
35	...
36	```
37
38	## Workflow
39
40	### 1. Planning
41
42	When exploring the codebase, use the project's domain glossary so that test names and interface vocabulary match the project's language, and respect ADRs in the area you're touching.
43
44	Before writing any code:
45
46	- [ ] Confirm with user what interface changes are needed
47	- [ ] Confirm with user which behaviors to test (prioritize)
48	- [ ] Identify opportunities for [deep modules](deep-modules.md) (small interface, deep implementation)
49	- [ ] Design interfaces for [testability](interface-design.md)
50	- [ ] List the behaviors to test (not implementation steps)
51	- [ ] Get user approval on the plan
52
53	Ask: "What should the public interface look like? Which behaviors are most important to test?"
54
55	You can't test everything. Confirm with the user exactly which behaviors matter most. Focus testing effort on critical paths and complex logic, not every possible edge case.
56
57	### 2. Tracer Bullet
58
59	Write ONE test that confirms ONE thing about the system:
60
61	```
62	RED: Write test for first behavior → test fails
63	GREEN: Write minimal code to pass → test passes
64	```
65
66	This is your tracer bullet - proves the path works end-to-end.
67
68	### 3. Incremental Loop
69
70	For each remaining behavior:
71
72	```
73	RED: Write next test → fails
74	GREEN: Minimal code to pass → passes
75	```
76
77	Rules:
78
79	- One test at a time
80	- Only enough code to pass current test
81	- Don't anticipate future tests
82	- Keep tests focused on observable behavior
83
84	### 4. Refactor
85
86	After all tests pass, look for [refactor candidates](refactoring.md):
87
88	- [ ] Extract duplication
89	- [ ] Deepen modules (move complexity behind simple interfaces)
90	- [ ] Apply SOLID principles where natural
91	- [ ] Consider what new code reveals about existing code
92	- [ ] Run tests after each refactor step
93
94	Never refactor while RED. Get to GREEN first.
95
96	## Checklist Per Cycle
97
98	```
99	[ ] Test describes behavior, not implementation
100	[ ] Test uses public interface only
101	[ ] Test would survive internal refactor
102	[ ] Code is minimal for this test
103	[ ] No speculative features added
104	```

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tdd

560stars68forks

View on GitHub

How to install tdd?

stevesolun/ctx/tdd

$npx -y skills add stevesolun/ctx --skill tdd

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Test-Driven Development
2
3	## Philosophy
4
5	Core principle: Tests should verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't.
6
7	Good tests are integration-style: they exercise real code paths through public APIs. They describe _what_ the system does, not _how_ it does it. A good test reads like a specification - "user can checkout with valid cart" tells you exactly what capability exists. These tests survive refactors because they don't care about internal structure.
8
9	Bad tests are coupled to implementation. They mock internal collaborators, test private methods, or verify through external means (like querying a database directly instead of using the interface). The warning sign: your test breaks when you refactor, but behavior hasn't changed. If you rename an internal function and tests fail, those tests were testing implementation, not behavior.
10
11	See [tests.md](tests.md) for examples and [mocking.md](mocking.md) for mocking guidelines.
12
13	## Anti-Pattern: Horizontal Slices
14
15	DO NOT write all tests first, then all implementation. This is "horizontal slicing" - treating RED as "write all tests" and GREEN as "write all code."
16
17	This produces crap tests:
18
19	- Tests written in bulk test _imagined_ behavior, not _actual_ behavior
20	- You end up testing the _shape_ of things (data structures, function signatures) rather than user-facing behavior
21	- Tests become insensitive to real changes - they pass when behavior breaks, fail when behavior is fine
22	- You outrun your headlights, committing to test structure before understanding the implementation
23
24	Correct approach: Vertical slices via tracer bullets. One test → one implementation → repeat. Each test responds to what you learned from the previous cycle. Because you just wrote the code, you know exactly what behavior matters and how to verify it.
25
26	```
27	WRONG (horizontal):
28	RED: test1, test2, test3, test4, test5
29	GREEN: impl1, impl2, impl3, impl4, impl5
30
31	RIGHT (vertical):
32	RED→GREEN: test1→impl1
33	RED→GREEN: test2→impl2
34	RED→GREEN: test3→impl3
35	...
36	```
37
38	## Workflow
39
40	### 1. Planning
41
42	When exploring the codebase, use the project's domain glossary so that test names and interface vocabulary match the project's language, and respect ADRs in the area you're touching.
43
44	Before writing any code:
45
46	- [ ] Confirm with user what interface changes are needed
47	- [ ] Confirm with user which behaviors to test (prioritize)
48	- [ ] Identify opportunities for [deep modules](deep-modules.md) (small interface, deep implementation)
49	- [ ] Design interfaces for [testability](interface-design.md)
50	- [ ] List the behaviors to test (not implementation steps)
51	- [ ] Get user approval on the plan
52
53	Ask: "What should the public interface look like? Which behaviors are most important to test?"
54
55	You can't test everything. Confirm with the user exactly which behaviors matter most. Focus testing effort on critical paths and complex logic, not every possible edge case.
56
57	### 2. Tracer Bullet
58
59	Write ONE test that confirms ONE thing about the system:
60
61	```
62	RED: Write test for first behavior → test fails
63	GREEN: Write minimal code to pass → test passes
64	```
65
66	This is your tracer bullet - proves the path works end-to-end.
67
68	### 3. Incremental Loop
69
70	For each remaining behavior:
71
72	```
73	RED: Write next test → fails
74	GREEN: Minimal code to pass → passes
75	```
76
77	Rules:
78
79	- One test at a time
80	- Only enough code to pass current test
81	- Don't anticipate future tests
82	- Keep tests focused on observable behavior
83
84	### 4. Refactor
85
86	After all tests pass, look for [refactor candidates](refactoring.md):
87
88	- [ ] Extract duplication
89	- [ ] Deepen modules (move complexity behind simple interfaces)
90	- [ ] Apply SOLID principles where natural
91	- [ ] Consider what new code reveals about existing code
92	- [ ] Run tests after each refactor step
93
94	Never refactor while RED. Get to GREEN first.
95
96	## Checklist Per Cycle
97
98	```
99	[ ] Test describes behavior, not implementation
100	[ ] Test uses public interface only
101	[ ] Test would survive internal refactor
102	[ ] Code is minimal for this test
103	[ ] No speculative features added
104	```

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6 picks

Type