Refactor tests for command groups
Refactor tests for command groups

We should not rely on default commands, because they can be removed or
shuffled around in the future. Use our custom command in the tests.

Also, add a test that ensures that a group does not disappear after the
call without parameters.

Reported-by: John Mair <97ea805dc4e09eb53a5875179c78385b35058fc0@gmail.com>
Signed-off-by: Kyrylo Silin <6129bf6f04030cd1423e4f3df28402e79fbf30a4@gmail.com>

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