Add test for CouchbaseDocument.verifyValueType

[lacinoire]

Hey 😊 I want to contribute a test. Curious to hear what you think!

(I wrote this test as part of a research study at TU Delft. Find out more)

---

• [x] You have read the Spring Data contribution guidelines.
• [ ] There is a ticket in the bug tracker for the project in our JIRA. This is a "trivial" change to test code which I believe is too simple for a jira ticket?
• [x] You use the code formatters provided here and have them applied to your changes. Don’t submit any formatting related changes.
• [x] You submit test cases (unit or integration tests) that back your changes.
• [ ] You added yourself as author in the headers of the classes you touched. Amend the date range in the Apache license header if needed. For new types, add the license header (copy from another file and set the current year only). No, but other contributors to the test classes also didn't

[lacinoire]

Thank you for having a look. I incorporated your suggestions and moved the test case too 🙂

[mikereiche]

Thanks.

Also required is an issue for this, and to add your name to the @authors of the class. Regardless if it is trivial or others didn't.

And the last line in the "commit comment" needs to be

Closes #.

[lacinoire]

Okay! I added the author reference, a new issue and the reference to closing it.

Rebased & squashed to a new commit with the proper message to keep the history clean 🙂