diff --git a/test/isPrime.test.js b/test/isPrime.test.js
index 2e967fce3..e64fdde4e 100644
--- a/test/isPrime.test.js
+++ b/test/isPrime.test.js
@@ -7,3 +7,6 @@ test('isPrime is a Function', () => {
 test('passed number is a prime', () => {
   expect(isPrime(11)).toBeTruthy();
 });
+test('passed number is not a prime', () => {
+  expect(isPrime(10)).toBeFalsy();
+});
diff --git a/test/memoize.test.js b/test/memoize.test.js
index fd906727b..886935616 100644
--- a/test/memoize.test.js
+++ b/test/memoize.test.js
@@ -12,6 +12,9 @@ test('Function works properly', () => {
 test('Function works properly', () => {
   expect(square(3)).toBe(9);
 });
+test('Function works properly, cache stores values (coverage)', () => {
+  expect(square(3)).toBe(9);
+});
 test('Cache stores values', () => {
   expect(Array.from(square.cache)).toEqual([[2, 4], [3, 9]]);
 });
diff --git a/test/nodeListToArray.test.js b/test/nodeListToArray.test.js
index b775d168a..f8d9006af 100644
--- a/test/nodeListToArray.test.js
+++ b/test/nodeListToArray.test.js
@@ -4,3 +4,6 @@ const {nodeListToArray} = require('./_30s.js');
 test('nodeListToArray is a Function', () => {
   expect(nodeListToArray).toBeInstanceOf(Function);
 });
+test('nodeListToArray returns an array of proper length', () => {
+  expect(nodeListToArray(document.childNodes).length).toBe(2);
+});
diff --git a/test/off.test.js b/test/off.test.js
index 0da5e9d94..a6fd08674 100644
--- a/test/off.test.js
+++ b/test/off.test.js
@@ -4,3 +4,31 @@ const {off} = require('./_30s.js');
 test('off is a Function', () => {
   expect(off).toBeInstanceOf(Function);
 });
+test('off removes an event listener', () => {
+  let el = document.createElement('div');
+  let val = false;
+  const fn = () => val = true;
+  el.addEventListener('click', fn);
+  off(el, 'click', fn);
+  var clickEvent = new MouseEvent('click', {
+    'view': window,
+    'bubbles': true,
+    'cancelable': false
+  });
+  el.dispatchEvent(clickEvent);
+  expect(val).toBeFalsy();
+});
+test('off removes an event listener', () => {
+  let el = document.createElement('div');
+  let val = false;
+  const fn = () => val = true;
+  el.addEventListener('click', fn);
+  off(el, 'click', fn, {});
+  var clickEvent = new MouseEvent('click', {
+    'view': window,
+    'bubbles': true,
+    'cancelable': false
+  });
+  el.dispatchEvent(clickEvent);
+  expect(val).toBeFalsy();
+});
diff --git a/test/on.test.js b/test/on.test.js
index c757e9592..3acdff31f 100644
--- a/test/on.test.js
+++ b/test/on.test.js
@@ -4,3 +4,30 @@ const {on} = require('./_30s.js');
 test('on is a Function', () => {
   expect(on).toBeInstanceOf(Function);
 });
+test('on creates an event listener', () => {
+  let el = document.createElement('div');
+  let val = false;
+  const fn = () => val = true;
+  on(el, 'click', fn);
+  var clickEvent = new MouseEvent('click', {
+    'view': window,
+    'bubbles': true,
+    'cancelable': false
+  });
+  el.dispatchEvent(clickEvent);
+  expect(val).toBeTruthy();
+});
+test('on creates an event listener', () => {
+  let el = document.createElement('div');
+  document.body.appendChild(el);
+  let val = false;
+  const fn = () => val = true;
+  on(document.body, 'click', fn, { target: 'div' });
+  var clickEvent = new MouseEvent('click', {
+    'view': window,
+    'bubbles': true,
+    'cancelable': false
+  });
+  el.dispatchEvent(clickEvent);
+  expect(val).toBeTruthy();
+});