Run XCTests from inside a Swift Playground

RunTests.swift

import XCTest

public func runTests(inClass testClass: XCTestCase.Type) {
    let testSuite = testClass.defaultTestSuite
    testSuite.run()
    guard let testRun = testSuite.testRun else {
        preconditionFailure("Couldn't run tests in \(testClass)")
    }
    let failCount = testRun.totalFailureCount
    guard failCount == 0 else {
        preconditionFailure("\(testClass) had \(failCount) failures")
    }
}

// MARK: - Usage

class SampleTestCase: XCTestCase {
    func testCanary() {
        XCTAssert(true)
    }
}
runTests(inClass: SampleTestCase.self)