public function testToPostfix()
{
$exp = new Expression();
$this->assertEquals(['a', 'b', '&', 'c', '|'], $exp->toPostfix("a&b|c"));
$this->assertEquals(['aw', 'bw', '&', 'cw', '|'], $exp->toPostfix("aw&bw|cw"));
$this->assertEquals(['a', 'b', 'd', 'c', '&', '|', '&'], $exp->toPostfix("a&(b|d&c)"));
$this->assertEquals(['a', 'b', '|'], $exp->toPostfix("a|b"));
$this->assertEquals(['great', 'awsome', '|'], $exp->toPostfix("great|awsome"));
$this->assertEquals(['great', 'awsome', '|'], $exp->toPostfix("great or awsome"));
$this->assertEquals(['great', 'awsome', '&'], $exp->toPostfix("great awsome"));
$this->assertEquals(['email', 'test', '&', 'com', '&'], $exp->toPostfix("email test com"));
$this->assertEquals(['email', 'test', '&', 'com', '&'], $exp->toPostfix("*****@*****.**"));
$this->assertEquals(['first', 'last', '&', 'something', 'else', '&', '|'], $exp->toPostfix("(first last) or (something else)"));
}