Migrating "Testing Lambdas" to MDX

[vcampitelli]

I found it easier to duplicate the branch from #2340 and fix things there as merging or rebasing were kind of complicated.

I've compared both articles a few times before opening this PR.

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• To see the specific tasks where the Asana app for GitHub is being used, see below:
  • https://app.asana.com/0/0/1205281000171129
  • https://app.asana.com/0/0/1206094054455342

[mark-robustelli]

Get stuck with error message. Think I found out why. Was logged in to admin app and tried to log in as richard too.

[mark-robustelli]

Everything else worked well. It is just the login test that I am having issues with now.
test login returns JWT with "Goodbye World"
not ok 1 TypeError: login is not a function
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operator: error
stack: |-
TypeError: login is not a function

[mark-robustelli]

Overall a bit better. Still seeing some of the deprecation messages and got one error I had to fix, but I was able to get all the way through it with 6 tests passing.

[vcampitelli]

@mark-robustelli I've pushed some changes and this is now ready for re-review

[mark-robustelli]

All looks good, only 2 issues. 1) Still getting the deprecation warnings but I think you said we have to update the library to get rid of them so I think that is OK. 2) In the commands to install the testing framework I get errors from the copy and paste because of the comments. Please find another way to comment.

[mark-robustelli]

LGTM