diff --git a/test/byteSize.test.js b/test/byteSize.test.js
index 1199b5a3b..963aada9f 100644
--- a/test/byteSize.test.js
+++ b/test/byteSize.test.js
@@ -1,4 +1,5 @@
 const expect = require('expect');
+const { byteSize } = require('./_30s.js');
 const Blob = class {
   constructor(s) {
     return {
@@ -6,7 +7,6 @@ const Blob = class {
     };
   }
 };
-const byteSize = str => new Blob([str]).size;
 
 test('byteSize is a Function', () => {
   expect(byteSize).toBeInstanceOf(Function);
diff --git a/test/copyToClipboard.test.js b/test/copyToClipboard.test.js
index 27bbd402e..e9b66c361 100644
--- a/test/copyToClipboard.test.js
+++ b/test/copyToClipboard.test.js
@@ -4,3 +4,28 @@ const {copyToClipboard} = require('./_30s.js');
 test('copyToClipboard is a Function', () => {
   expect(copyToClipboard).toBeInstanceOf(Function);
 });
+test('copyToClipboard does not throw errors', () => {
+  document.getSelection = function () {
+    return {
+      rangeCount: 0,
+      removeAllRanges() { return; },
+      addRange(x) { return x; }
+    };
+  }
+  document.execCommand = function (x) { return x; }
+
+  expect(copyToClipboard('hi')).toBe(undefined);
+});
+test('copyToClipboard does not throw errors', () => {
+  document.getSelection = function () {
+    return {
+      rangeCount: 1,
+      getRangeAt(x) { return x+1; },
+      removeAllRanges() { return; },
+      addRange(x) { return x; }
+    };
+  }
+  document.execCommand = function (x) { return x; }
+
+  expect(copyToClipboard('hi')).toBe(undefined);
+});
diff --git a/test/once.test.js b/test/once.test.js
index 158d164f8..1dd65d3a6 100644
--- a/test/once.test.js
+++ b/test/once.test.js
@@ -4,6 +4,11 @@ const {once} = require('./_30s.js');
 test('once is a Function', () => {
   expect(once).toBeInstanceOf(Function);
 });
-test('once is a Function', () => {
+test('once returns Function', () => {
   expect(typeof once(x => 10)).toBe('function');
 });
+test('once returns the result only once', () => {
+  let onced = once(x => x);
+  expect(onced(10)).toBe(10);
+  expect(onced(10)).toBe(undefined);
+});
diff --git a/test/permutations.test.js b/test/permutations.test.js
index f0d8764ab..dc92a0232 100644
--- a/test/permutations.test.js
+++ b/test/permutations.test.js
@@ -14,3 +14,6 @@ test('Generates all permutations of an array', () => {
     [5, 33, 1]
   ]);
 });
+test('Generates all permutations of an array', () => {
+  expect(permutations([1])).toEqual([1]);
+});
diff --git a/test/pluralize.test.js b/test/pluralize.test.js
index 0dbe882cd..e732b500e 100644
--- a/test/pluralize.test.js
+++ b/test/pluralize.test.js
@@ -13,9 +13,12 @@ test('Produces the singular of the word', () => {
 test('Produces the plural of the word', () => {
   expect(pluralize(2, 'apple')).toBe('apples');
 });
-test('Prodices the defined plural of the word', () => {
+test('Produces the defined plural of the word', () => {
   expect(pluralize(2, 'person', 'people')).toBe('people');
 });
+test('Produces the defined plural of the word', () => {
+  expect(pluralize(1, 'person', 'people')).toBe('person');
+});
 const PLURALS = {
   person: 'people',
   radius: 'radii'
diff --git a/test/prettyBytes.test.js b/test/prettyBytes.test.js
index 954713d42..76fde2e88 100644
--- a/test/prettyBytes.test.js
+++ b/test/prettyBytes.test.js
@@ -13,3 +13,9 @@ test('Converts a number in bytes to a human-readable string.', () => {
 test('Converts a number in bytes to a human-readable string.', () => {
   expect(prettyBytes(123456789, 3, false)).toBe('123MB');
 });
+test('Converts a number in bytes to a human-readable string.', () => {
+  expect(prettyBytes(0, 3, false)).toBe('0B');
+});
+test('Converts a number in bytes to a human-readable string.', () => {
+  expect(prettyBytes(0, 3, true)).toBe('0 B');
+});