     func testEmptyPop() {
         var stack = Stack<String>()
         stack.pop()
-        XCTAssertTrue(stack.isEmpty)
+        XCTAssertTrue(stack.isEmpty())
         XCTAssertEqual(stack.count, 0)
         XCTAssertEqual(stack.top(), nil)
         XCTAssertNil(stack.pop())

//

import XCTest
@testable import Stack

class StackTests: XCTestCase {
    func testEmptyIntStack() {
        var stack = Stack<Int>()
        XCTAssertTrue(stack.isEmpty)
        XCTAssertEqual(stack.count, 0)
        XCTAssertEqual(stack.top(), nil)
        XCTAssertNil(stack.pop())

    func testPushAndPop() {
        var stack = Stack<String>()
        stack.push("i")
        XCTAssertFalse(stack.isEmpty())
        XCTAssertEqual(stack.count, 1)
        XCTAssertEqual(stack.top(), "i")
        
        let result = stack.pop()
        XCTAssertEqual(result, "i")
        XCTAssertTrue(stack.isEmpty())
        XCTAssertEqual(stack.count, 0)
        XCTAssertEqual(stack.top(), nil)
        XCTAssertNil(stack.pop())
