diff --git a/package.json b/package.json
index 9b664feaa..5dc6f865f 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,7 @@
         "lint": "npx semistandard --fix",
         "sass": "sass scss/custom.scss client/style.css --style compressed",
         "start": "node server.js",
+        "test": "node --test",
         "webpack": "webpack --config webpack.config.js"
     },
     "dependencies": {
diff --git a/test/get-bonus-part-label.test.js b/test/get-bonus-part-label.test.js
new file mode 100644
index 000000000..aad6b2f5a
--- /dev/null
+++ b/test/get-bonus-part-label.test.js
@@ -0,0 +1,33 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import getBonusPartLabel from '../client/scripts/utilities/get-bonus-part-label.js';
+
+test('returns default value and empty difficulty when bonus is undefined', () => {
+  assert.equal(getBonusPartLabel(undefined, 0), '[10]');
+});
+
+test('uses bonus value when present', () => {
+  const bonus = { values: [15, 10, 5] };
+  assert.equal(getBonusPartLabel(bonus, 0), '[15]');
+  assert.equal(getBonusPartLabel(bonus, 2), '[5]');
+});
+
+test('uses difficultyModifier when present', () => {
+  const bonus = { values: [10, 10, 10], difficultyModifiers: ['e', 'm', 'h'] };
+  assert.equal(getBonusPartLabel(bonus, 0), '[10e]');
+  assert.equal(getBonusPartLabel(bonus, 2), '[10h]');
+});
+
+test('falls back to defaultValue when index has no value', () => {
+  const bonus = { values: [10] };
+  assert.equal(getBonusPartLabel(bonus, 5), '[10]');
+});
+
+test('uses custom defaultValue and defaultDifficulty', () => {
+  assert.equal(getBonusPartLabel(undefined, 0, 20, 'e'), '[20e]');
+});
+
+test('returns label with no difficulty when difficultyModifiers absent', () => {
+  const bonus = { values: [10, 10, 10] };
+  assert.equal(getBonusPartLabel(bonus, 1), '[10]');
+});
diff --git a/test/merge-two-sorted-arrays.test.js b/test/merge-two-sorted-arrays.test.js
new file mode 100644
index 000000000..511bd43d2
--- /dev/null
+++ b/test/merge-two-sorted-arrays.test.js
@@ -0,0 +1,43 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import mergeTwoSortedArrays from '../server/merge-two-sorted-arrays.js';
+
+const byId = x => x.id;
+const keepFirst = (a, _b) => a;
+const sumValues = (a, b) => ({ id: a.id, v: a.v + b.v });
+
+test('merges two non-overlapping sorted arrays', () => {
+  const a = [{ id: 1 }, { id: 3 }];
+  const b = [{ id: 2 }, { id: 4 }];
+  const result = mergeTwoSortedArrays(a, b, byId, keepFirst);
+  assert.deepEqual(result.map(x => x.id), [1, 2, 3, 4]);
+});
+
+test('combines elements with duplicate keys via combineFunction', () => {
+  const a = [{ id: 1, v: 10 }, { id: 2, v: 20 }];
+  const b = [{ id: 2, v: 5 }, { id: 3, v: 30 }];
+  const result = mergeTwoSortedArrays(a, b, byId, sumValues);
+  assert.deepEqual(result, [{ id: 1, v: 10 }, { id: 2, v: 25 }, { id: 3, v: 30 }]);
+});
+
+test('returns copy of array1 when array2 is empty', () => {
+  const a = [{ id: 1 }, { id: 2 }];
+  const result = mergeTwoSortedArrays(a, [], byId, keepFirst);
+  assert.deepEqual(result.map(x => x.id), [1, 2]);
+});
+
+test('returns copy of array2 when array1 is empty', () => {
+  const b = [{ id: 5 }, { id: 7 }];
+  const result = mergeTwoSortedArrays([], b, byId, keepFirst);
+  assert.deepEqual(result.map(x => x.id), [5, 7]);
+});
+
+test('returns empty array when both inputs are empty', () => {
+  const result = mergeTwoSortedArrays([], [], byId, keepFirst);
+  assert.deepEqual(result, []);
+});
+
+test('handles single-element arrays', () => {
+  const result = mergeTwoSortedArrays([{ id: 3 }], [{ id: 1 }], byId, keepFirst);
+  assert.deepEqual(result.map(x => x.id), [1, 3]);
+});
diff --git a/test/strings.test.js b/test/strings.test.js
new file mode 100644
index 000000000..c7b82453f
--- /dev/null
+++ b/test/strings.test.js
@@ -0,0 +1,55 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { escapeHTML, kebabCase, removeParentheses, titleCase } from '../client/scripts/utilities/strings.js';
+
+test('escapeHTML escapes &, <, >, ", and single quotes', () => {
+  assert.equal(escapeHTML('a & b'), 'a &amp; b');
+  assert.equal(escapeHTML('<b>bold</b>'), '&lt;b&gt;bold&lt;/b&gt;');
+  assert.equal(escapeHTML('"quoted"'), '&quot;quoted&quot;');
+  assert.equal(escapeHTML("it's"), 'it&#039;s');
+});
+
+test('escapeHTML returns undefined for undefined input', () => {
+  assert.equal(escapeHTML(undefined), undefined);
+});
+
+test('escapeHTML returns empty string unchanged', () => {
+  assert.equal(escapeHTML(''), '');
+});
+
+test('kebabCase converts spaces to hyphens and lowercases', () => {
+  assert.equal(kebabCase('Hello World'), 'hello-world');
+  assert.equal(kebabCase('multiple   spaces'), 'multiple-spaces');
+  assert.equal(kebabCase('ALLCAPS'), 'allcaps');
+});
+
+test('kebabCase handles already-lowercase single word', () => {
+  assert.equal(kebabCase('hello'), 'hello');
+});
+
+test('removeParentheses removes round parens content', () => {
+  // The function removes the parens and their content but does not collapse
+  // the surrounding spaces — a trailing trim is the only whitespace cleanup.
+  assert.equal(removeParentheses('foo (bar) baz'), 'foo  baz');
+});
+
+test('removeParentheses removes square bracket content', () => {
+  assert.equal(removeParentheses('foo [bar] baz'), 'foo  baz');
+});
+
+test('removeParentheses trims surrounding whitespace', () => {
+  assert.equal(removeParentheses('  hello  '), 'hello');
+});
+
+test('removeParentheses returns string unchanged when no parens', () => {
+  assert.equal(removeParentheses('plain string'), 'plain string');
+});
+
+test('titleCase capitalises first letter of each word', () => {
+  assert.equal(titleCase('hello-world'), 'Hello World');
+  assert.equal(titleCase('foo-bar-baz'), 'Foo Bar Baz');
+});
+
+test('titleCase handles single word without hyphen', () => {
+  assert.equal(titleCase('hello'), 'Hello');
+});