Testing Pitfalls: The Trapdoors in Your “Perfect” Code

“The only thing worse than no tests is trusting bad tests.”
— Ancient Prairie Dev Wisdom

Testing isn’t just about writing code that checks your code. It’s about trusting the code that checks your code. And that trust? It’s fragile, like Saskatoon Wi-Fi during a snowstorm.

Let’s break down the mistakes that sabotage regression testing, ruin CI/CD pipelines, and make your TA’s eye twitch during grading.

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🕳️ Pitfall 1: The False Positive

This is when your test says “everything’s fine,” but your app is screaming in production.

It’s the worst kind of betrayal — like getting ghosted by your own code.

🔥 Example:

java
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@Test
public void testSomething() {
    assertTrue(true);
}

Bruh. This test will always pass. It’s as useful as a frozen doorknob in February.

💡 Fix:

Write meaningful assertions. Know what you’re checking for — then actually check for it.

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🪤 Pitfall 2: The False Negative

Your test fails — but not because your code is broken. It fails because your test is.

Maybe you:

• Hardcoded a date

• Depended on external APIs

• Forgot to mock something

And now your test fails at 12:01 AM and you’re crying in Louis’ wondering why.

💡 Fix:

Make your tests deterministic and isolated. No randomness. No API calls. No “sometimes it fails, sometimes it doesn’t” chaos.

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🔁 Pitfall 3: Testing the Wrong Thing

Your test runs perfectly. Passes every time. But it doesn’t test the thing you think it does.

Example:

java
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@Test
public void shouldAddUser() {
    UserManager manager = new UserManager();
    manager.addUser("Alice");
    // no assertion 🙃
}

That’s just running code, not testing it. It’s like showing up to the gym and just sitting on the bench.

💡 Fix:

Always assert specific outcomes — not just that the method didn’t crash.

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💤 Pitfall 4: Over-Mocking Everything

Mocking is great — until it’s all you do.

If you mock literally everything, you’re not testing real behavior. You’re testing your mock setup, not your logic.

💡 Fix:

Mock only what you need to isolate. Let your actual code breathe where possible.

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😬 Pitfall 5: Ignoring Edge Cases

Sure, you tested that your snowplow app works when it's -10°C. But what happens at -50°C? What if no plows are available? What if the map is null?

If you’re only testing the “happy path,” you’re doing it wrong.

💡 Fix:

Write sad path tests. Rage-test your app like it's being used by someone in the worst-case scenario — probably during a blackout in February.

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🧪 Pitfall 6: Duplicate Tests

You have 5 tests that all do the same thing.

You feel good because your test coverage is 98%, but really, you’ve just copy-pasted one good test four times and called it a day.

💡 Fix:

Focus on diverse and targeted test cases. If multiple tests cover the same code in the same way, delete the extras.

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🧼 Pitfall 7: Dirty Tests (No Cleanup)

Tests that leave behind:

• Temporary files

• Mock data in databases

• Open sockets

• Memory leaks

...are why your test suite randomly fails on the CI server but works fine locally.

💡 Fix:

Use @AfterEach or @AfterAll to clean up. Or better yet, use proper setup/teardown frameworks like @BeforeEach.

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🔕 Pitfall 8: Silent Failures

Some devs (👀 you know who you are) write tests with empty catch blocks:

java
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try {
    someRiskyThing();
} catch (Exception e) {
    // ignore
}

Now your test passes even when it should have exploded.

💡 Fix:

Never swallow exceptions silently. Either assert them, or let them fail loud and proud.

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🧱 Pitfall 9: Rigid Test Logic

Tests that break every time you refactor good code are not your friends.

They’re the clingy ex of your codebase.

Hardcoded values, tightly coupled logic, or excessive test duplication makes your test suite fragile.

💡 Fix:

Test behavior, not implementation. Don’t test how the code works, test what it’s supposed to do.

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📉 Pitfall 10: Ignoring Failing Tests

The worst habit in all of CS:

“It’s just that one test. I think it’s flaky.”

And then you disable it. Then a few more. Then suddenly your whole test suite is just a suggestion.

💡 Fix:

Fix. Your. Tests.
Flaky tests need refactoring. Not excuses.

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🧠 Bonus: Pitfalls in Regression Testing Context

In regression testing, these pitfalls are 100x worse because you’re running old tests to catch new bugs. If your tests are flaky, meaningless, or broken?

• Bugs slip through undetected

• You ship regressions

• Your team loses trust in testing

• Your test suite becomes code theater — all performance, no substance

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🎓 TL;DR (Too Long, Didn’t Pitfall-Proof):

Avoid these traps:

• 🚫 False positives & negatives

• 💤 Empty or pointless tests

• 🧟‍♂️ Over-mocking

• ❄️ Ignoring edge cases

• 🔁 Duplicate coverage

• 🧼 Dirty state

• 😶 Silent failures

• 🏗️ Fragile test structure

• 😬 Ignoring red tests

Your test suite is only useful if it’s honest, sharp, and low-key paranoid.

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💡 Final Words from the Tunnel

Good regression testing isn’t just about coverage — it’s about trust.
Trust that your tests mean what they say.
Trust that when they pass, your app is actually working.

Avoid these pitfalls, and your test suite won’t just pass — it’ll protect.