python - How to assert variable content in unit test (Flask, Python3, Nose2) -

i have flask app page content comes global variable. i'm trying set unit testing assert data, can't seem local variable work:

test_string = foo  self.assertin(b['test_string'], response.data) 

fails with:

nameerror: name 'b' not defined 

if reference plain variable:

self.assertin(test_string, response.data) 

i expected failure:

typeerror: bytes-like object required, not 'str' 

the test succeeds if hard-code variable data test, i'd rather not have update test if variable changes. missing here?

the problem bytes literal prefix b:

bytes literals prefixed 'b' or 'b'; produce instance of bytes type instead of str type. may contain ascii characters; bytes numeric value of 128 or greater must expressed escapes.

while sounds bytesprefix = bytes type, not seem work if data comes variable.

the solution change b prefix bytes functionbytes, states:

bytes objects can created literals, see string , bytes literals.

so while appear interchangeable, not case!

for use case, had specify encoding type bytes function.

here working syntax original post's example:

self.assertin(bytes(test_string, "utf-8"), response.data) 

thanks goes john gordon suggested switching bytes in comments, never officially answered. after few days, i'll go ahead , close out now.