You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: test_stringchar.rb
    path of file: ./repos/ruby/test/ruby
    
    the code of the file until where you have to start completion: # frozen_string_
    
  def test_bang
    s = "aBc"
    s.upcase
    assert_equal("aBc", s)
    s.upcase!
    assert_equal("ABC", s)

    s = "aBc"
    s.downcase
    assert_equal("aBc", s)
    s.downcase!
    assert_equal("abc", s)

    s = "aBc"
    s.swapcase
    assert_equal("aBc", s)
    s.swapcase!
    assert_equal("AbC", s)

    s = "aBc"
    s.capitalize
    assert_equal("aBc", s)
    s.capitalize!
    assert_equal("Abc", s)

    s = "aBc"
    s.tr("a-z", "A-Z")
    assert_equal("aBc", s)
    s.tr!("a-z", "A-Z")
    assert_equal("ABC", s)

    s = "aaBBcc"
    s.tr_s("a-z", "A-Z")
    assert_equal("aaBBcc", s)
    s.tr_s!("a-z", "A-Z")
    assert_equal("ABBC", s)

    s = "aaBBcc"
    s.squeeze("a-z")
    assert_equal("aaBBcc", s)
    s.squeeze!("a-z")
    assert_equal("aBBc", s)

    s = "aaBBcc"
    s.delete("a-z")
    assert_equal("aaBBcc", s)
    s.delete!("a-z")
    assert_equal("BB", s)
  end