How to check if text appears on page in rails functional test?

Without specifying a tag:

assert_match "this is the test line", response.body

I think you're just looking for:

assert_select "p", "this is the test line"

See the docs for more info about assert_select.

Note that the line above depends on the text being wrapped in a <p> tag, and being a literal match. If it's in another tag, you'll need to specify the correct selector. If you'd like to match on a Regex, that is also supported, via:

assert_select "p", /test line/

Note that this will not be very performant, as it will scan through all <p>'s in your document. Consider a more tightly specified selector, like a class or ID on the element you're targeting.