```ruby
require_relative '../../spec_helper'

describe "mathn" do
  ruby_version_is "2.5" do
    it "is no longer part of the standard library" do
      -> { require "mathn" }.should raise_error(LoadError)
    end
  end
end
```

Improve spec for mathn on Ruby 2.5+
user
```ruby
require_relative '../../spec_helper'

describe "mathn" do
  ruby_version_is "2.5" do
    it "is no longer part of the standard library" do
      -> {
        require "mathn"
      }.should raise_error(LoadError) { |e|
        e.path.should == 'mathn'
      }
    end
  end
end
```
assistant