Del:scissors: all things about tests

Time flies! 😭  Due to our new work assignments, there is REALLY no more time to do any things for tests. Hope to have time to do sth about this in the future.

One more thing (written in `guide.md` already):
Our development does not involve changing the original code in package `bugzilla`. What we do is just adding sth new. So we try ensuring is that once there is no problem in original *python-bugzilla*, the code added by us will also work well.

Author: SonicStark

bugzilla/_mi.py

@@ -30,7 +30,6 @@
 import requests.exceptions
 
 import bugzilla
-from ._cli import _is_unittest_debug
 from ._cli import open_without_clobber
 from ._cli import _setup_root_parser
 from ._cli import _setup_action_new_parser
@@ -230,9 +229,6 @@ def level_logging(debug, verbose):
     else:
         log.setLevel(logging.WARN)
 
-    if _is_unittest_debug():
-        log.setLevel(logging.DEBUG)  # pragma: no cover
-
 
 ##################
 # Option parsing #

docs/README.md

@@ -58,13 +58,10 @@ It introduces how our **MI** is built based on the previous **CLI** and its appl
 /python-bugzilla
 ](https://github.com/python-bugzilla/python-bugzilla), reading it will enable you to quickly understand and use this project.
 
-### `tests.md`
-
-Describe these things about running the unit test.
-
-### `assets`: demos & charts
+### `assets`
 
 | Item | Description |
 |------|-------------|
 | workflow.drawio     | It is drawn with [jgraph/drawio](https://github.com/jgraph/drawio) and shows how we maintain this project. |
 | workflow.drawio.png | Rendered from `workflow.drawio` for using in `python-bugzilla-mi/README.md`. |
+|demo_frontend.py|...|

docs/guide.md

@@ -177,18 +177,6 @@ def _get_timeout(self):
     return float(envtimeout or DEFAULT_TIMEOUT)
 ```
 
-### 2.3.3. `__BUGZILLA_UNITTEST_DEBUG`
-
-It may be changed by `tests.conftest.pytest_configure`, but only affects the return value of `bugzilla._cli._is_unittest_debug`. It seems that the only function it has is to ensure that global log output level is `DEBUG`.
-
-:warning: As the author of this guide I cannot accurately determine its use at present, please use with care if you need.
-
-### 2.3.4. `__BUGZILLA_UNITTEST`
-
-Referred only in `tests.__init__` as `os.environ["__BUGZILLA_UNITTEST"] = "1"`. It is suspected that this is a bug, the statement is more likely to be `os.environ["__BUGZILLA_UNITTEST_DEBUG"] = "1"`.
-
-:warning: As the author of this guide I cannot accurately determine its use at present, please use with care if you need.
-
 ## 2.4 Exit *MI*
 
 It is recommand that do <kbd>Ctrl</kbd>+<kbd>C</kbd> or equivalent operation. The try-except mechanism in `MI` would catch `KeyboardInterrupt` and print