nes-emu/cpu/Stack.spec.js

A NES emulator

"use strict";

var _Stack = _interopRequireDefault(require("./Stack"));
var _constants = _interopRequireDefault(require("../constants"));
var _createTestContext = _interopRequireDefault(require("../helpers/createTestContext"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
const should = require("chai").Should();
describe("Stack", () => {
  let cpu, memory, context, stack;
  beforeEach(() => {
    ({
      cpu,
      memory,
      context
    } = (0, _createTestContext.default)());
    stack = new _Stack.default().loadContext(context);
    cpu.sp.value = 0xff;
  });
  it("can push and pop values", () => {
    stack.push(23);
    stack.push(24);
    stack.push(25);
    stack.pop().should.equal(25);
    stack.pop().should.equal(24);
    stack.pop().should.equal(23);
  });
  it("can push and pop 16-bit values", () => {
    stack.push2Bytes(0xfe30);
    stack.push2Bytes(0xcd45);
    stack.push2Bytes(0x1234);
    stack.pop2Bytes().should.equal(0x1234);
    stack.pop2Bytes().should.equal(0xcd45);
    stack.pop2Bytes().should.equal(0xfe30);
  });
  it("updates the memory and sp on push", () => {
    stack.push(23);
    memory.readAt(_constants.default.CPU_STACK_START_ADDRESS + 0xff).should.equal(23);
    cpu.sp.value.should.equal(0xfe);
  });
  it("reads from the memory and updates sp on pop", () => {
    stack.push(23);
    memory.writeAt(_constants.default.CPU_STACK_START_ADDRESS + 0xff, 30);
    stack.pop().should.equal(30);
    cpu.sp.value.should.equal(0xff);
  });
  it("ignores stack underflows", () => {
    memory.writeAt(0x0100, 32);
    stack.pop().should.equal(32);
    cpu.sp.value.should.equal(0);
  });
  it("ignores stack overflows", () => {
    cpu.sp.value = 0;
    stack.push(32);
    memory.readAt(0x0100).should.equal(32);
    cpu.sp.value.should.equal(0xff);
  });
});