---
alwaysApply: true
---

# 21. TESTING IS MANDATORY

Every meaningful implementation change requires tests.

At minimum test:

```text
normal case
failure case
boundary case
insufficient evidence
```

For semantic models, also test the boundaries between object types.

For PCB analysis, explicitly test:

```text
Pad
Via
Track
Zone
```

as distinct semantic entities.

---

# 22. TESTS MUST BE STRICT AND ABSOLUTE

Periscope tests are not advisory.

A test must define the exact expected behavior.

Do not use vague assertions such as:

```text
result is reasonable
result is not empty
analysis completed
```

when an exact result can be established.

Prefer assertions such as:

```text
expected object type == Via
expected pad count == 24
expected finding count == 0
expected finding code == X
expected severity == ERROR
expected confidence == HIGH
```

Where deterministic exact values are available, test them exactly.

Do not weaken tests merely to make an implementation pass.

Do not modify expected results to accommodate incorrect implementation behavior.

---

# 23. REGRESSION TEST FOR EVERY BUG

Every fixed bug must become a regression test.

Required sequence:

```text
BUG
 ↓
REPRODUCE
 ↓
TEST FAILS
 ↓
FIX
 ↓
TEST PASSES
 ↓
FULL REGRESSION
```

A bug fix is not complete until the original failure is permanently represented by a test.

---

# 24. TEST THE NEGATIVE CASE

Do not test only:

```text
valid → pass
```

Also test:

```text
invalid → fail
```

and ensure that genuine errors remain detectable.

For example, if fixing:

```text
24 datasheet pins
24 footprint pads
N vias
```

verify that:

```text
24 datasheet pins
23 footprint pads
```

still produces a real mismatch.

The fix must remove false positives without suppressing true positives.

---

# 26. NO WEAKENING TESTS TO CLOSE A PHASE

Do not:

* delete failing tests;
* weaken assertions;
* skip tests;
* mark tests expected-to-fail;
* suppress failures;
* change expected values without engineering justification;

simply to make a macro-phase pass.

If a test exposes a real implementation problem, fix the implementation.

If the requirement itself is wrong, change the requirement explicitly and document why.

---