[JsonPatch] Add test operation support

[rynowak]

From @kirthik on March 20, 2015 9:37

Test operation in code today does not compare anything. Removing the TODO from code. Pasting code snippet for reference.

var conversionResultTuple = PropertyHelpers.ConvertToActualType(
                typeOfFinalPropertyAtPathLocation,
                operation.value);

            // conversion successful
            if (conversionResultTuple.CanBeConverted)
            {
                // COMPARE - TODO
            }
            else
            {
                throw new JsonPatchException<T>(operation,
                    string.Format("Patch failed: provided value is invalid for property type at location path: {0}",
                        operation.path),
                    objectToApplyTo);
            }

Copied from original issue: aspnet/Mvc#2218

[rynowak]

From @danroth27 on April 1, 2015 16:16

@kirthik Do we currently return a 400 level error response if someone tries a test operation?

[rynowak]

From @kirthik on April 1, 2015 17:4

No. We don't. It does nothing today.

[Levitikon217]

Curious.. Will the Test Operator be implemented at some point? If so, do you know when? I'm requiring functionality that the test operator provides and I'm considering my options here.

[zygimantas]

As a workaround I use:

// JSON.stringify([{ op: "test", path: "/key", value: "key_value"}])
// [FromBody] JsonPatchDocument<CustomRequestModel> jsonPatchDocument

var operation = jsonPatchDocument.Operations.SingleOrDefault(
a => a.OperationType == OperationType.Test &&
a.path.Equals("/key", System.StringComparison.CurrentCultureIgnoreCase));

// (string)operation.value