Compare strings in swift unit test

How do you test whether 2 strings are equal in a swift unit test? I've tried the == operator but it doesn't recognize it:

import XCTest
@testable import MyProject

class MyProject: XCTestCase {

override func setUp() {
    super.setUp()
    // Put setup code here. This method is called before the invocation of each test method in the class.
}

override func tearDown() {
    // Put teardown code here. This method is called after the invocation of each test method in the class.
    super.tearDown()
}

func testExample() {
    // This is an example of a functional test case.
    // Use XCTAssert and related functions to verify your tests produce the correct results.
    XCTAssertNil(nil, "This test works")
}

func toJSONTest() {
    let currentLocation = deviceLocation(timestamp: "2015-11-02 16:32:15 +0000",latitude: "40.2736577695212",longitude: "-111.715408331498")
    var MyProjectStatuses = [MyProjectStatus(id: "", currentLocation: currentLocation)]
    let json = ""
    XCTAssertTrue(json == "")
}

func testPerformanceExample() {
    // This is an example of a performance test case.
    self.measureBlock {
        // Put the code you want to measure the time of here.
    }
}

}

And the actual method being tested from MyProject.swift:

func toJSON ()->String{
    var json = ""
    json = "{\"myproject_status\":"
    json = json + "{\"id\":\"" + self.Id + "\""
    return json 
}

This part:

XCTAssertTrue(json == "")

Throws:

Operator is not a known binary operator