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Code Smell 276 - Untested Regular Expressions

by Maximiliano ContieriOctober 27th, 2024

Too Long; Didn't Read

Use clear and concise regular expressions, and test them thoroughly.

featured image - Code Smell 276 - Untested Regular Expressions

Regex Without Tests is Asking for Trouble - Don't be lazy. It is free with AI!

TL;DR: Use clear and concise regular expressions, and test them thoroughly.

Problems

Readability
No test cases
Missed edge cases
Debugging challenges
Unclear failures
Hidden defects

Solutions

Ask your favorite AI to write test cases
Break down complex regular expressions into smaller, more readable parts.
Check edge cases
Validate outputs
Refactor regex once you created the tests
Improve the Error Messages

Context

Regular expressions are powerful but tricky.

If you write a regex without tests, you're asking for unexpected errors.

If you write a cryptic regex and skip automated testing, you could miss important cases, causing security issues or user frustration.

Sample Code

Wrong

public class PasswordValidator {
    public static boolean isValidPassword(String password) {
        return password.matches(
            "^(?=.*[a-z])(?=.*[A-Z])(?=.*\\d)[a-zA-Z\\d]{8,}$");
        // This is a cryptic Regular Expression
    }
}

Right

import java.util.ArrayList;
import java.util.List;

public class PasswordValidator {
    public static List<String> validatePassword(String password) {
        List<String> errors = new ArrayList<>();

        if (password.length() < 8) {
            errors.add(
                "Password must be at least 8 characters long.");
        }
        if (!password.matches(".*[A-Z].*")) {
            errors.add(
                "Password must contain at least one uppercase letter.");
        }
        if (!password.matches(".*[a-z].*")) {
            errors.add(
                "Password must contain at least one lowercase letter.");
        }
        if (!password.matches(".*\\d.*")) {
            errors.add(
                "Password must contain at least one digit.");
        }
        if (errors.isEmpty()) {
            errors.add(
                "Password is valid.");
        }
        return errors;
        // You no longer need a Regular Expression!!
    }
}

import static org.junit.Assert.*;
import org.junit.Test;

public class PasswordValidatorTest {
    // Now you have a lot of tests
    // You can use a Regular Expression,
    // a String Validator
    // an External Library
    // Whatever you want as long as it passes the tests!

    @Test
    public void testValidPassword() {
        List<String> result = 
            PasswordValidator.validatePassword(
            "StrongPass1");
        assertEquals("Password is valid.", result.get(0));
    }

    @Test
    public void testTooShortPassword() {
        List<String> result = PasswordValidator.validatePassword(
            "Short1");
        assertTrue(result.contains(
            "Password must be at least 8 characters long."));
    }

    @Test
    public void testNoUppercase() {
        List<String> result = PasswordValidator.validatePassword(
            "nouppercase1");
        assertTrue(
            result.contains(
                "Password must contain at least one uppercase letter."));
    }

    @Test
    public void testNoLowercase() {
        List<String> result = PasswordValidator.validatePassword(
            "NOLOWERCASE1");
        assertTrue(result.contains(
            "Password must contain at least one lowercase letter."));
    }

    @Test
    public void testNoNumber() {
        List<String> result = PasswordValidator.validatePassword(
            "NoNumberPass");
        assertTrue(result.contains(
            "Password must contain at least one digit."));
    }
}