test: implement pending tests leftover from TS rewrite (#315)
test: implement pending tests leftover from TS rewrite (#315)

This commit implements 4 of the 6 pending tests that were not completed
during the TypeScript rewrite. The two tests that were not implemented
were (one for each of v1 and v03):

```
it("returns a JSON string even if format is invalid");
```

I don't really know what that's supposed to be/mean, so I removed them.

Fixes: https://github.com/cloudevents/sdk-javascript/issues/232

Signed-off-by: Lance Ball <637094cbcafd6c4c397ebad24eca1a25fa2cf312@redhat.com>
cloudevents/sdk-javascript,cloudevents/sdk-javascript