What branch to test continuous integration?

For a new project, the version control branch structure is as follows,

* develop
* feature
* master

I am confused if I should write tests on a different branch, say a new branch test branch or just in the existing develop branch? Is it a good practice to write unit tests in feature or develop branch and integration tests in a test branch. If not where should the tests go to? what are the good and bad things about keeping a separate test branch? My develop branch will be committed and pushed frequently.

thank you for any answer.