Allow specifying strings when using path-based expectJSON

[PyvesB]

When calling expectJSON with the optional path argument, you can't specify a string as the jsonTest parameter.

Example response:

{
  "key1": {
    "key2": "value1"
  },
  "key3": "value2"
}

Calling expectJSON('key1.key2', 'value1'), is not possible, as the second argument value1 is not an object.

expectContainsJSON could be used as an alternative, however, its syntax isn't as concise especially with more complex JSON structures, and the error messages are much more vague as we're checking that a structure contains another. It would be nice to have something that gets to the point by strictly comparing a string at a given path with an expected string.

Support for this could either be implemented in expectJSON itself or as a separate helper function.

See the discussions here for more context.

Cheers,

Pyves