diff --git a/08_calculator/calculator.spec.js b/08_calculator/calculator.spec.js
index 48b08c9..d3502e4 100644
--- a/08_calculator/calculator.spec.js
+++ b/08_calculator/calculator.spec.js
@@ -12,6 +12,17 @@ describe('add', () => {
   test.skip('adds positive numbers', () => {
     expect(calculator.add(2, 6)).toBe(8);
   });
+
+   // test.skip negative numbers
+   test.skip('adds negative numbers', () => {
+    expect(calculator.add(-5, -10)).toBe(-15);
+  });
+
+  // test.skip decimals
+  test.skip('adds decimals', () => {
+    expect(calculator.add(0.5, 1.5)).toBeCloseTo(2); 
+  });
+
 });
 
 describe('subtract', () => {
@@ -36,6 +47,16 @@ describe('sum', () => {
   test.skip('computes the sum of an array of many numbers', () => {
     expect(calculator.sum([1, 3, 5, 7, 9])).toBe(25);
   });
+
+  // test subtracting negative number
+  test.skip('subtracts negative number', () => {
+    expect(calculator.subtract(10, -5)).toBe(15);
+  });
+
+  // test decimals
+  test.skip('subtracts decimals', () => {
+    expect(calculator.subtract(1.5, 0.5)).toBeCloseTo(1);
+  });
 });
 
 describe('multiply', () => {
@@ -46,12 +67,23 @@ describe('multiply', () => {
   test.skip('multiplies several numbers', () => {
     expect(calculator.multiply([2, 4, 6, 8, 10, 12, 14])).toBe(645120);
   });
+
+  // test 0
+  test.skip('multiplies by 0', () => {
+    expect(calculator.multiply([2, 0, 5])).toBe(0); 
+  });
 });
 
 describe('power', () => {
   test.skip('raises one number to the power of another number', () => {
     expect(calculator.power(4, 3)).toBe(64); // 4 to third power is 64
   });
+
+
+  // test power of 0
+  test.skip('0 to the power of anything is 0', () => {
+    expect(calculator.power(0, 5)).toBe(0);
+  });
 });
 
 describe('factorial', () => {
@@ -74,4 +106,14 @@ describe('factorial', () => {
   test.skip('computes the factorial of 10', () => {
     expect(calculator.factorial(10)).toBe(3628800);
   });
+
+   // test non-integer
+   test.skip('throws error for non-integer', () => {
+    expect(() => calculator.factorial(1.5)).toThrow();
+  });
+
+  // test negative
+  test.skip('throws error for negative number', () => {
+    expect(() => calculator.factorial(-5)).toThrow(); 
+  });
 });