test: Add more scenarios for email address encoding

[2mt-heuser]

Fixes

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

Because the current test expected an exception in the middle of the scenario it did never actually reach the other assertions. (it stopped after setting null as name)
I extracted the error cases into their own respective tests and also added more cases for the other parts of the helper

It doesn't address everything in #606, but it's a step in the right direction.

[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

Hello @2mt-heuser,

Thanks again for the PR!

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