Git branching strategy integated with testing/QA process

The way we do it is the following:

We test on the feature branches after we merge the latest develop branch code on them. The main reason is that we do not want to "pollute" the develop branch code before a feature is accepted. In case a feature would not be accepted after testing but we would like to release other features already merged on develop that would be hell. Develop is a branch from which a release is made and thus should better be in a releasable state. The long version is that we test in many phases. More analytically:

1. Developer creates a feature branch for every new feature.
2. The feature branch is (automatically) deployed on our TEST environment with every commit for the developer to test.
3. When the developer is done with deployment and the feature is ready to be tested he merges the develop branch on the feature branch and deploys the feature branch that contains all the latest develop changes on TEST.
4. The tester tests on TEST. When he is done he "accepts" the story and merges the feature branch on develop. Since the developer had previously merged the develop branch on feature we normally don't expect too many conflicts. However, if that's the case the developer can help. This is a tricky step, I think the best way to avoid it is to keep features as small/specific as possible. Different features have to be eventually merged, one way or another. Of course the size of the team plays a role on this step's complexity.
5. The develop branch is also (automatically) deployed on TEST. We have a policy that even though the features branch builds can fail the develop branch should never fail.
6. Once we have reached a feature freeze we create a release from develop. This is automatically deployed on STAGING. Extensive end to end tests take place on there before the production deployment. (ok maybe I exaggerate a bit they are not very extensive but I think they should be). Ideally beta testers/colleagues i.e. real users should test there.

What do you think of this approach?

Before test, we merge the changes from the develop branch to the feature branch

No. Don't, especially if 'we' is the QA tester. Merging would involve resolving potential conflicts, which is best done by developers (they know their code), and not by QA tester (who should proceed to test as quickly as possible).

Make the developer do a rebase of his/her feature branch on top of devel, and push that feature branch (which has been validated by the developer as compiling and working on top of the most recent devel branch state).
That allows for:

• a very simple integration on the feature branch (trivial fast-forward merge).
• or, as recommended by Aspasia below in the comments, a pull request (GitHub) or merge request (GitLab): the maintainer does a merge between the feature PR/MR branch and develop, but only if not conflict are detected by GitHub/GitLab.

Each time the tester detects bug, he/she will report it to the developer and delete the current feature branch.
The developer can:

• fix the bug
• rebase on top of a recently fetched develop branch (again, to be sure that his/her code works in integration with other validated features)
• push the feature branch.

General idea: make sure the merge/integration part is done by the developer, leaving the testing to the QA.

The best approach is continuous integration, where the general idea is to merge the feature branches into the developer branch as frequently as possible. This reduces on the overhead of merging pains.

Rely on automated tests as much as possible, and have builds automatically kick off with unit tests by Jenkins. Have the developers do all the work with merging their changes into the main branch and provide unit tests for all their code.

The testers/QA can take participate in code reviews, check off on unit tests and write automated integration tests to be added to the regression suite as features are completed.

For more info check out this link.