I encountered the same problem, so I put the type of http verb to POST, I did the body, then I open with notepad++ the .webtest file.

Inside my test block I took the line starting with

<StringHttpBody

I went back in the solution, I put the test to PUT, the good verb, if at this point you save and you look again in notepad the file just display <formSomething with nothing inside, even after switching back to POST. So I closed the solution, I replace this line with the <StringHttpBody I saved, with the good content-type, and the body.

After reopening the solution, it was ok, the PUT test have now the good body and content-type.

Yes it's annoying :/

@stegriff [MSFT], @Sylvain Lucas

Thanks for your feedback.
I acknowledge that this is an issue. We are working on the fix, meanwhile can you please use the following workaround in step 5:

1. Create a blank WebTest

2. Create a new Web Services Request.
3. Change method to PUT or PATCH
4. Update String Body with the following info:
- Content Type: application/json
- String Body: {"blah":true}
5. Workaround step -- right click the String Body, click Copy from the context menu and Paste on the same tree node as in:

6. Run test

Sorry for the inconvenience.
Thanks, Ganesh.

This issue has been fixed and is now available in our latest update. You can download the update via the in-product notification or from here: https://visualstudio.microsoft.com/vs/ Thanks to all who provided feedback and solutions for this problem.