This content originally appeared on HackerNoon and was authored by Maximiliano Contieri
Don’t let test code sneak into production
TL;DR: Avoid adding isTesting or similar flags.
Problems 😔
- Leaky abstraction
- Non-Business code pollution
- Fragile Code
- Inconsistent behavior
- Hidden dependencies
- Difficult debugging
- Boolean flags
- Untrusted tests
- Production dependant code
Solutions 😃
- Remove behavior Ifs
- Use dependency injection
- Model external services (Don't mock them)
- Separate configurations
- Isolate test logic
- Maintain clean behavior boundaries
Refactorings ⚙️
https://hackernoon.com/refactoring-014-how-to-remove-if?embedable=true
Context 💬
When you add flags like isTesting, you mix testing and production code.
\ This creates hidden paths that are only active in tests.
\ Also, you don't cover real production code.
\ You risk shipping testing behavior to production, leading to bugs and unpredictable behavior.
Sample Code 📖
Wrong ❌
struct PaymentService {
is_testing: bool,
}
impl PaymentService {
fn process_payment(&self, amount: f64) {
if self.is_testing {
println!("Testing mode: Skipping real payment");
return;
}
println!("Processing payment of ${}", amount);
}
}
Right 👉
trait PaymentProcessor {
fn process(&self, amount: f64);
}
struct RealPaymentProcessor;
impl PaymentProcessor for RealPaymentProcessor {
fn process(&self, amount: f64) {
println!("Processing payment of ${}", amount);
}
}
struct TestingPaymentProcessor;
impl PaymentProcessor for TestingPaymentProcessor {
// Notice this is not a mock
fn process(&self, _: f64) {
println!("No payment: Skipping real transaction");
}
}
struct PaymentService<T: PaymentProcessor> {
processor: T,
}
impl<T: PaymentProcessor> PaymentService<T> {
fn process_payment(&self, amount: f64) {
self.processor.process(amount);
}
}
Detection 🔍
- [x] Semi-Automatic
You can detect this smell by looking for conditional flags like isTesting, environment == 'test', DEBUG_MODE, and idioms like these.
\ These indicate that testing behavior is leaking into the production code.
Tags 🏷️
- Testing
Level 🔋
- [x] Intermediate
Why the Bijection Is Important 🗺️
You need a clear separation between test and production code.
\ When you mix them, you break the one-to-one Bijection between real-world behavior and the program.
\ Since environments are real-world entities you need to explicitly model them in the MAPPER.
AI Generation 🤖
AI-generated code often introduces this smell when you use quick hacks for testing.
\ Some tools suggest flags like isTesting because they prioritize ease over proper design.
AI Detection 🥃
AI tools can catch this smell if you configure them to flag conditional logic based on testing states.
Try Them! 🛠
Remember: AI Assistants make lots of mistakes
Suggested Prompt: Remove IsTesting method and replace it by modeling the environments
| Without Proper Instructions | With Specific Instructions | |----|----| | ChatGPT | ChatGPT | | Claude | Claude | | Perplexity | Perplexity | | Copilot | Copilot | | Gemini | Gemini | | DeepSeek | DeepSeek | | Meta AI | Meta AI | | Qwen | Qwen |
Conclusion 🏁
Avoid using isTesting flags.
\ Use dependency injection and model the environments to keep test and production logic separate.
Relations 👩❤️💋👨
https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxii
https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xiii
https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-vi-cmj31om
https://hackernoon.com/code-smell-242-zombie-feature-flags?embedable=true
Disclaimer 📘
Code Smells are my opinion.
Credits 🙏
Photo by Christian Gertenbach on Unsplash
When you add testing flags, you undermine confidence in production.
Ward Cunningham
https://hackernoon.com/400-thought-provoking-software-engineering-quotes?embedable=true
This article is part of the CodeSmell Series.
https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-i-xqz3evd?embedable=true
\
This content originally appeared on HackerNoon and was authored by Maximiliano Contieri
Maximiliano Contieri | Sciencx (2025-03-06T21:29:12+00:00) Code Smell 293 – You Should Avoid Adding isTesting or Similar Flags. Retrieved from https://www.scien.cx/2025/03/06/code-smell-293-you-should-avoid-adding-istesting-or-similar-flags/
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