Function double_characters 

pub fn double_characters(input: &str) -> String

Randomly doubles some characters in the string.

Each alphabetic character has approximately a 33% chance of being doubled. This creates visually distinct text that tests input normalization and character repetition handling. Non-alphabetic characters are not doubled.

Use Cases

• Input Validation: Test if systems properly handle repeated characters
• Blue Team: Verify normalization and deduplication logic
• Red Team: Bypass simple length or pattern checks
• Data Quality: Test string comparison and matching algorithms

Examples

use redstr::double_characters;

let result = double_characters("test");
// Example output: "teesst" or "ttest" or "tesst" (varies each run)
assert!(result.len() >= 4);

// Test input validation
let username = double_characters("admin");
// Example: "aadmiin" or "addmin" or "admmin"

// Numbers are preserved
let mixed = double_characters("test123");
// Example: "ttesst123" (numbers unchanged)