Convert header h1-h6 markdown in php to html

markdownToPhp.php

<? php
function markdown_parser ($markdown) {
  $segments = explode('# ', trim($markdown), 2);
  if(count($segments)>1){
    //adding back the hash that explode removed, this simplifies the logic below
    $segments[0] = $segments[0].'#'; 
    
    //making sure that all are hashes and nothing else at the start of markdown
    $first_array = str_split($segments[0]);
    $unique = array_unique($first_array);
    // all are hashes and not more than 6
    if(count($unique) == 1 and strlen($segments[0]) < 7){
      //everything is good, make the html
      $header = 'h'.(string)strlen($segments[0]);
      return '<'.$header.'>'.trim($segments[1]).'</'.$header.'>';
    }
    
  }
  return $markdown;
}

class MarkdownParserSolution extends TestCase
{
    public function testBasicValidCases() {
      $this->assertSame("<h1>header</h1>", markdown_parser("# header"));
      $this->assertSame("<h2>smaller header</h2>", markdown_parser("## smaller header"));
    }
    public function testBasicInvalidCases() {
      $this->assertSame("#Invalid", markdown_parser("#Invalid"));
      $this->assertSame("dbcdddd# Invalid", markdown_parser("dbcdddd# Invalid"));
      $this->assertSame("ddddd# Invalid", markdown_parser("ddddd# Invalid"));
    }
}