SignpostTestObserver.swift

import XCTest
import os.log
import os.signpost

// Add to your test suite "Info.plist": "Principal class" => "$(PRODUCT_NAME).TestObserver"
class SignpostTestObserver: NSObject, XCTestObservation {

    lazy var log: OSLog = {
            return OSLog(subsystem: "net.davelyon.os-log-test", category: "example")
    }()

    override init() {
        super.init()

        // XCTestObservation keeps a strong reference to observers
        XCTestObservationCenter.shared.addTestObserver(self)
    }

    // MARK: - Test Bundle

    func testBundleWillStart(_ testBundle: Bundle) {
        let id = OSSignpostID(log: log, object: testBundle)
        os_signpost(.begin, log: log, name: "test bundle", signpostID: id, "%@", testBundle.description)
    }

    public func testBundleDidFinish(_ testBundle: Bundle) {
        let id = OSSignpostID(log: log, object: testBundle)
        os_signpost(.end, log: log, name: "test bundle", signpostID: id, "%@", testBundle.description)
    }

    // MARK: - Test Suite

    func testSuiteWillStart(_ testSuite: XCTestSuite) {
        let id = OSSignpostID(log: log, object: testSuite)
        os_signpost(.begin, log: log, name: "test suite", signpostID: id, "%@", testSuite.name)
    }

    func testSuiteDidFinish(_ testSuite: XCTestSuite) {
        let id = OSSignpostID(log: log, object: testSuite)
        os_signpost(.end, log: log, name: "test suite", signpostID: id, "%@, duration: %f", testSuite.name, testSuite.testRun!.testDuration)
    }

    func testSuite(_ testSuite: XCTestSuite, didFailWithDescription description: String,
                   inFile filePath: String?, atLine lineNumber: Int) {
        let id = OSSignpostID(log: log, object: testSuite)
        os_signpost(.event, log: log, name: "test suite failure", signpostID: id)
    }

    // MARK: - Test Case

    func testCaseWillStart(_ testCase: XCTestCase) {
        let id = OSSignpostID(log: log, object: testCase)
        os_signpost(.begin, log: log, name: "test case", signpostID: id, "%@", testCase.name)
    }

    func testCaseDidFinish(_ testCase: XCTestCase) {
        let id = OSSignpostID(log: log, object: testCase)
        os_signpost(.end, log: log, name: "test case", signpostID: id, "%@, duration: %f", testCase.name, testCase.testRun!.testDuration)
    }

    func testCase(_ testCase: XCTestCase, didFailWithDescription description: String,
                  inFile filePath: String?, atLine lineNumber: Int) {
        let id = OSSignpostID(log: log, object: testCase)
        os_signpost(.event, log: log, name: "test case failure", signpostID: id)
    }

}