ruby on rails - Deprecation warning for integration test on http header -

i'm using minitest , in integration test have line:

assert_select response.header['content-type'], "application/json" 

it responds with:

deprecation warning: assertion not run because of invalid css selector.
unexpected ';' after '[#nokogiri::css::node:0x000000064b2e58 @type=:child_selector, @value=[#nokogiri::css::node:0x000000064b3268 @type=:element_name, @value=["application"]>, #nokogiri::css::node:0x000000064b2ef8 @type=:element_name, @value=["json"]>]>]' (called block in class:sessionstest> @ (byebug):1)

does understand causes , how (alternatively) test header?

assert_select used check expectation in dom object, view result.

what should use in case assert_equal. note that, in assert_equal, expectation first argument.

assert_equal "application/json", response.header['content-type']