Finish testing mathematics

examples/basic-math/src/arithmetic.js

@@ -1,9 +1,28 @@
 export const add = (a, b) => {
+  if (typeof a === 'string') a = Number(a);
+  if (typeof b === 'string') b = Number(b);
+
+  if (isNaN(a)) throw new Error('The first argument is not a number');
+  if (isNaN(b)) throw new Error('The second argument is not a number');
+
   return a + b;
 };
 
-export const subtract = () => {};
+export const subtract = (a = 0, b = 0) => {
+  if (Array.isArray(a)) {
+    a = a.reduce((a, b) => {
+      return a - b;
+    });
+  }
 
-export const multiply = () => {};
+  return a - b;
+};
 
-export const divide = () => {};
+export const multiply = (a, b) => {
+  return a * b;
+};
+
+export const divide = (a, b) => {
+  if (b === 0) return null;
+  return a / b;
+};

examples/basic-math/src/arithmetic.test.js

@@ -1,14 +1,72 @@
 import { describe, it, expect } from 'vitest';
-import { add } from './arithmetic.js';
+import { add, subtract, multiply, divide } from './arithmetic.js';
 
 describe('add', () => {
   it('should add two positive numbers', () => {
     expect(add(2, 2)).toBe(4);
   });
+
+  it('should add two negative numbers', () => {
+    expect(add(-2, -2)).toBe(-4);
   });
 
-describe.todo('subtract', () => {});
+  it('should parse strings into numbers', () => {
+    expect(add('1', '1')).toBe(2);
+  });
 
-describe.todo('multiply', () => {});
+  it('should get real angry if you give it a first argument that cannot be parsed into a number', () => {
+    expect(() => add('potato', 2)).toThrow('not a number');
+  });
 
-describe.todo('divide', () => {});
+  it('should get real angry if you give it a second argument that cannot be parsed into a number', () => {
+    expect(() => add(2, 'potato')).toThrow('not a number');
+  });
+
+  it('should throw if the first argument is not a number', () => {
+    expect(() => add(NaN, 2)).toThrow('not a number');
+  });
+
+  it('should handle floating point math as best it can', () => {
+    expect(add(1.0000001, 2.0000004)).toBeCloseTo(3.0, 1);
+  });
+});
+
+describe('subtract', () => {
+  it('should subtract one number from the other', () => {
+    expect(subtract(4, 2)).toBe(2);
+  });
+
+  it('should accept and subtract all of the numbers', () => {
+    expect(subtract([10, 5], 2)).toBe(3);
+  });
+
+  it('should default undefined values to 0', () => {
+    expect(subtract(3)).toBe(3);
+    expect(subtract(undefined, 3)).toBe(-3);
+  });
+
+  it('should default to zero if either argument is null', () => {
+    expect(subtract(3, null)).toBe(3);
+    expect(subtract(null, 3)).toBe(-3);
+  });
+});
+
+describe('multiply', () => {
+  it('should multiply two numbers', () => {
+    expect(multiply(3, 2)).toBe(6);
+  });
+});
+
+describe('divide', () => {
+  it('should divide two numbers', () => {
+    expect(divide(10, 2)).toBe(5);
+  });
+
+  it('should return null if dividing by zero', () => {
+    expect(divide(10, 0)).toBeNull();
+  });
+
+  it('should return zero if dividing by Infinity', () => {
+    expect(divide(10, Infinity)).toBe(0);
+  });
+});