Bring the little test over but I'll probably ditch Jest in this project.

__tests__/buttons.spec.js

@@ -0,0 +1,113 @@
+const { ButtonMachine } = require('../../src/node_modules/buttons');
+
+const run_code = (expecting, code, debug=false) => {
+  let machine = new ButtonMachine(code);
+
+  machine.run(debug);
+
+  expect(machine.stack_top).toBe(expecting);
+
+  return machine;
+}
+
+it('Can do addition', () => {
+  run_code(3, [
+    ['PUSH', 1],
+    ['PUSH', 2],
+    ['ADD'],
+  ])
+});
+
+it('Can do subtraction', () => {
+  run_code(1, [
+    ['PUSH', 2],
+    ['PUSH', 1],
+    ['SUB'],
+  ])
+})
+
+it('Can do multiplication', () => {
+  run_code(20, [
+    ['PUSH', 10],
+    ['PUSH', 2],
+    ['MUL'],
+  ])
+})
+
+it('Can do division', () => {
+  run_code(5, [
+    ['PUSH', 10],
+    ['PUSH', 2],
+    ['DIV'],
+  ])
+})
+
+it('Can do modulus', () => {
+  run_code(0, [
+    ['PUSH', 10],
+    ['PUSH', 2],
+    ['MOD'],
+  ])
+})
+
+it('Can loop until the end of ticks', () => {
+  run_code(43, [
+    ['PUSH', 1],
+    ['PUSH', 1],
+    ['ADD'],
+    ['JUMP', 1]
+  ]);
+});
+
+
+it('Can do zero test for jump', () => {
+  run_code(0, [
+    ['PUSH', 20], // start at 20
+    ['PUSH', 1],  // decrement by 1
+    ['SUB'],      
+    ['JZ', 5],    // if we're at 0 jumps to the end
+    ['JUMP', 1]   // the previous test fails so it jumps to loop again
+  ]);
+});
+
+
+it('Can do NOT zero test for jump', () => {
+  run_code(-19, [
+    ['PUSH', -20], // start at 20
+    ['PUSH', 1],  // decrement by 1
+    ['ADD'],      
+    ['JNZ', 5],    // if we're at 0 jumps to the end
+    ['JUMP', 1]    // the previous test fails so it jumps to loop again
+  ]);
+});
+
+it('Can store and restor', () => {
+  run_code(150, [
+    ['PUSH', 100],    // start with 100
+    ['STOR', 'AX'], // put it in the regA register
+    ['PUSH', 50],     // push 50 on too
+    ['ADD'],          // add those for 150
+    ['RSTOR', 'AX'],// recover the original 100
+    ['SUB']           // sub and should be 150
+  ]);
+});
+
+it('Halts on bad registers', () => {
+  run_code(0, [
+    ['PUSH', 0],
+    ['STOR', 'AX'],
+    ['RSTOR', 'BAD NAME'], // should cause a halt here
+    ['PUSH', 100],
+    ['ADD']
+  ]);
+});
+
+it('Can halt on purpose', () => {
+  let machine = run_code(0, [
+   ['PUSH', 0],
+   ['HALT', 'Done on purpose.']
+  ]);
+
+  expect(machine.halted).toBe(true);
+  expect(machine.error).toBe('Done on purpose.');
+});