diff --git a/test/inRange.test.js b/test/inRange.test.js
index 9a93aa20f..c4bfa03c2 100644
--- a/test/inRange.test.js
+++ b/test/inRange.test.js
@@ -7,6 +7,9 @@ test('inRange is a Function', () => {
 test('The given number falls within the given range', () => {
   expect(inRange(3, 2, 5)).toBeTruthy();
 });
+test('The given number falls within the given range (reverse)', () => {
+  expect(inRange(3, 5, 2)).toBeTruthy();
+});
 test('The given number falls within the given range', () => {
   expect(inRange(3, 4)).toBeTruthy();
 });
diff --git a/test/initialize2DArray.test.js b/test/initialize2DArray.test.js
index d520752c5..41700908d 100644
--- a/test/initialize2DArray.test.js
+++ b/test/initialize2DArray.test.js
@@ -7,3 +7,6 @@ test('initialize2DArray is a Function', () => {
 test('Initializes a 2D array of given width and height and value', () => {
   expect(initialize2DArray(2, 2, 0)).toEqual([[0, 0], [0, 0]]);
 });
+test('Initializes a 2D array of given width and height and value (no fill)', () => {
+  expect(initialize2DArray(2, 2)).toEqual([[null, null], [null, null]]);
+});
diff --git a/test/initializeArrayWithValues.test.js b/test/initializeArrayWithValues.test.js
index d47e6f60c..c1f75cd0a 100644
--- a/test/initializeArrayWithValues.test.js
+++ b/test/initializeArrayWithValues.test.js
@@ -7,3 +7,6 @@ test('initializeArrayWithValues is a Function', () => {
 test('Initializes and fills an array with the specified values', () => {
   expect(initializeArrayWithValues(5, 2)).toEqual([2, 2, 2, 2, 2]);
 });
+test('Initializes and fills an array with the specified values (no fill)', () => {
+  expect(initializeArrayWithValues(5)).toEqual([0, 0, 0, 0, 0]);
+});
diff --git a/test/isBrowser.test.js b/test/isBrowser.test.js
index 359dfd8d8..ec513860f 100644
--- a/test/isBrowser.test.js
+++ b/test/isBrowser.test.js
@@ -4,3 +4,6 @@ const {isBrowser} = require('./_30s.js');
 test('isBrowser is a Function', () => {
   expect(isBrowser).toBeInstanceOf(Function);
 });
+test('isBrowser is a Function', () => {
+  expect(typeof isBrowser()).toBe('boolean');
+});