psh: add help command test

[damianloew]

Description

psh: add help command test

Motivation and Context

JIRA: PD-77

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (list targets here).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[mateusz-bloch]

Well-structured and should serve its purpose efficiently

However, I'm wondering if it's the intended effect that, regardless of the argument given to the help function, it's always displayed? If so, I don't see any other test cases, except maybe a test could be added to check, for example, if the function displayed "Unknown command!" with HELP written in uppercase."

[github-actions]

Unit Test Results

5 957 tests  +8   5 304 ✔️ +8   30m 32s ⏱️ - 2m 0s
   333 suites +8      653 💤 ±0 
       1 files   ±0          0 ❌ ±0 

Results for commit 4d5ed29. ± Comparison against base commit a37c915.