Make "removeDuplicatedCharacters" PSR-12 friendly and add unit tests

Strings/RemoveDuplicatedCharacters.php

@@ -1,29 +1,33 @@
 <?php
+
+declare(strict_types=1);
+
 /**
- * The function loops through each character in the input string.
- * It uses an array $seen to keep track of characters that have already been added to the output string.
- * If a character hasn't been seen, it is appended to the result string, and the character is marked as seen.
- * The function returns the modified string with duplicate characters removed.
+ * Removes duplicate characters from a string, retaining only the first occurrence of each character.
+ *
+ * @param string $inputString The input string from which duplicates will be removed.
+ * @return string The modified string with duplicate characters removed.
  */
 
- function removeDuplicatedCharacters($inputString) {
+function removeDuplicatedCharacters(string $inputString): string
+{
     // Initialize an empty array to keep track of seen characters
     $seen = [];
-    
+
     // Initialize an empty string for the result
     $result = '';
 
     // Loop through each character in the input string
     for ($i = 0; $i < strlen($inputString); $i++) {
         $char = $inputString[$i];
-        
+
         // Check if the character has already been seen
-        if (!in_array($char, $seen)) {
+        if (!in_array($char, $seen, true)) {
             // Add the character to the result and mark it as seen
             $result .= $char;
             $seen[] = $char;
         }
     }
-    
+
     return $result;
-}
+}

composer.json

@@ -13,11 +13,10 @@
     "ext-json": "*"
   },
   "require-dev": {
-    "phpunit/phpunit": "^9",
+    "phpunit/phpunit": "^9.6",
     "squizlabs/php_codesniffer": "^3.7"
   },
   "scripts": {
     "test": "vendor/bin/phpunit tests"
   }
 }
-

tests/Strings/RemoveDuplicatedCharactersTest.php

@@ -0,0 +1,71 @@
+<?php
+
+declare(strict_types=1);
+
+require_once __DIR__ . '/../../vendor/autoload.php';
+require_once __DIR__ . '/../../Strings/RemoveDuplicatedCharacters.php';
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Unit tests for the removeDuplicatedCharacters function.
+ * To run test: ./vendor/bin/phpunit tests/strings/RemoveDuplicatedCharactersTest.php
+ */
+final class RemoveDuplicatedCharactersTest extends TestCase
+{
+    /**
+     * Test with a string that has multiple duplicates.
+     */
+    public function testStringWithDuplicates(): void
+    {
+        $this->assertSame('progamin', removeDuplicatedCharacters('programming'));
+    }
+
+    /**
+     * Test with a string that has no duplicates.
+     */
+    public function testStringWithoutDuplicates(): void
+    {
+        $this->assertSame('abc', removeDuplicatedCharacters('abc'));
+    }
+
+    /**
+     * Test with an empty string.
+     */
+    public function testEmptyString(): void
+    {
+        $this->assertSame('', removeDuplicatedCharacters(''));
+    }
+
+    /**
+     * Test with a string containing only one character repeated.
+     */
+    public function testSingleCharacterRepeated(): void
+    {
+        $this->assertSame('a', removeDuplicatedCharacters('aaaaa'));
+    }
+
+    /**
+     * Test with special characters.
+     */
+    public function testStringWithSpecialCharacters(): void
+    {
+        $this->assertSame('ab!@', removeDuplicatedCharacters('aabb!!@@'));
+    }
+
+    /**
+     * Test with a string containing spaces.
+     */
+    public function testStringWithSpaces(): void
+    {
+        $this->assertSame('a b', removeDuplicatedCharacters('a a a b b'));
+    }
+
+    /**
+     * Test with a string containing mixed case characters.
+     */
+    public function testStringWithMixedCase(): void
+    {
+        $this->assertSame('aAbB', removeDuplicatedCharacters('aAaAaAbBbB'));
+    }
+}