diff --git a/src/app/plugins/custom-emoji/PackImageReader.test.ts b/src/app/plugins/custom-emoji/PackImageReader.test.ts
new file mode 100644
index 000000000..3005bd109
--- /dev/null
+++ b/src/app/plugins/custom-emoji/PackImageReader.test.ts
@@ -0,0 +1,92 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { PackImageReader } from './PackImageReader';
+import { ImageUsage, PackImage } from './types';
+
+test('fromPackImage returns undefined when url is missing or not a string', () => {
+  assert.equal(PackImageReader.fromPackImage('cat', {} as unknown as PackImage), undefined);
+  assert.equal(
+    PackImageReader.fromPackImage('cat', { url: 123 } as unknown as PackImage),
+    undefined,
+  );
+});
+
+test('fromPackImage builds a reader with shortcode and url', () => {
+  const reader = PackImageReader.fromPackImage('cat', { url: 'mxc://x/cat' });
+  assert.ok(reader);
+  assert.equal(reader?.shortcode, 'cat');
+  assert.equal(reader?.url, 'mxc://x/cat');
+});
+
+test('body reads only string values', () => {
+  assert.equal(PackImageReader.fromPackImage('c', { url: 'u', body: 'Cat' })?.body, 'Cat');
+  assert.equal(PackImageReader.fromPackImage('c', { url: 'u' })?.body, undefined);
+  assert.equal(
+    PackImageReader.fromPackImage('c', { url: 'u', body: 5 } as unknown as PackImage)?.body,
+    undefined,
+  );
+});
+
+test('info is passed through unchanged', () => {
+  const info = { w: 10, h: 10 };
+  assert.equal(
+    PackImageReader.fromPackImage('c', { url: 'u', info } as unknown as PackImage)?.info,
+    info,
+  );
+  assert.equal(PackImageReader.fromPackImage('c', { url: 'u' })?.info, undefined);
+});
+
+test('usage filters to known values and returns undefined when none/non-array', () => {
+  assert.equal(PackImageReader.fromPackImage('c', { url: 'u' })?.usage, undefined);
+  assert.equal(
+    PackImageReader.fromPackImage('c', {
+      url: 'u',
+      usage: 'emoticon' as unknown as ImageUsage[],
+    })?.usage,
+    undefined,
+  );
+  assert.equal(
+    PackImageReader.fromPackImage('c', {
+      url: 'u',
+      usage: ['bogus'] as unknown as ImageUsage[],
+    })?.usage,
+    undefined,
+  );
+  assert.deepEqual(
+    PackImageReader.fromPackImage('c', { url: 'u', usage: [ImageUsage.Sticker] })?.usage,
+    [ImageUsage.Sticker],
+  );
+  assert.deepEqual(
+    PackImageReader.fromPackImage('c', {
+      url: 'u',
+      usage: [ImageUsage.Emoticon, 'x', ImageUsage.Sticker] as unknown as ImageUsage[],
+    })?.usage,
+    [ImageUsage.Emoticon, ImageUsage.Sticker],
+  );
+});
+
+test('content reconstructs the PackImage from url and raw image fields', () => {
+  const info = { w: 1, h: 1 };
+  const reader = PackImageReader.fromPackImage('c', {
+    url: 'u',
+    body: 'Cat',
+    usage: [ImageUsage.Emoticon],
+    info,
+  } as unknown as PackImage);
+  assert.deepEqual(reader?.content, {
+    url: 'u',
+    body: 'Cat',
+    usage: [ImageUsage.Emoticon],
+    info,
+  });
+});
+
+test('content preserves raw usage even when usage getter filters it', () => {
+  // content uses the raw image.usage, not the filtered usage getter
+  const reader = PackImageReader.fromPackImage('c', {
+    url: 'u',
+    usage: ['bogus'] as unknown as ImageUsage[],
+  });
+  assert.deepEqual(reader?.content.usage, ['bogus'] as unknown as ImageUsage[]);
+  assert.equal(reader?.usage, undefined);
+});
diff --git a/src/app/plugins/custom-emoji/PackImagesReader.test.ts b/src/app/plugins/custom-emoji/PackImagesReader.test.ts
new file mode 100644
index 000000000..6bb8169de
--- /dev/null
+++ b/src/app/plugins/custom-emoji/PackImagesReader.test.ts
@@ -0,0 +1,44 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { PackImagesReader } from './PackImagesReader';
+import { PackImages, ImageUsage } from './types';
+
+test('collection builds a shortcode -> reader map', () => {
+  const images: PackImages = {
+    cat: { url: 'mxc://x/cat', usage: [ImageUsage.Emoticon] },
+    dog: { url: 'mxc://x/dog' },
+  };
+  const reader = new PackImagesReader(images);
+  const collection = reader.collection;
+
+  assert.equal(collection.size, 2);
+  assert.equal(collection.get('cat')?.url, 'mxc://x/cat');
+  assert.equal(collection.get('cat')?.shortcode, 'cat');
+  assert.equal(collection.get('dog')?.url, 'mxc://x/dog');
+});
+
+test('collection drops invalid images (missing/non-string url)', () => {
+  const images = {
+    good: { url: 'mxc://x/good' },
+    noUrl: {},
+    badUrl: { url: 5 },
+  } as unknown as PackImages;
+  const collection = new PackImagesReader(images).collection;
+
+  assert.equal(collection.size, 1);
+  assert.ok(collection.has('good'));
+  assert.equal(collection.has('noUrl'), false);
+  assert.equal(collection.has('badUrl'), false);
+});
+
+test('collection of an empty image set is an empty map', () => {
+  const collection = new PackImagesReader({}).collection;
+  assert.equal(collection.size, 0);
+});
+
+test('collection is memoized (same Map instance returned)', () => {
+  const reader = new PackImagesReader({ cat: { url: 'u' } });
+  const first = reader.collection;
+  const second = reader.collection;
+  assert.equal(first, second);
+});
diff --git a/src/app/plugins/custom-emoji/PackMetaReader.test.ts b/src/app/plugins/custom-emoji/PackMetaReader.test.ts
new file mode 100644
index 000000000..ec8192179
--- /dev/null
+++ b/src/app/plugins/custom-emoji/PackMetaReader.test.ts
@@ -0,0 +1,48 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { PackMetaReader } from './PackMetaReader';
+import { ImageUsage, PackMeta } from './types';
+
+const reader = (meta: PackMeta) => new PackMetaReader(meta);
+
+test('name reads display_name only when it is a string', () => {
+  assert.equal(reader({ display_name: 'Cats' }).name, 'Cats');
+  assert.equal(reader({}).name, undefined);
+  assert.equal(reader({ display_name: 42 } as unknown as PackMeta).name, undefined);
+});
+
+test('avatar reads avatar_url only when it is a string', () => {
+  assert.equal(reader({ avatar_url: 'mxc://x/y' }).avatar, 'mxc://x/y');
+  assert.equal(reader({}).avatar, undefined);
+  assert.equal(reader({ avatar_url: {} } as unknown as PackMeta).avatar, undefined);
+});
+
+test('attribution reads attribution only when it is a string', () => {
+  assert.equal(reader({ attribution: 'me' }).attribution, 'me');
+  assert.equal(reader({}).attribution, undefined);
+  assert.equal(reader({ attribution: 0 } as unknown as PackMeta).attribution, undefined);
+});
+
+test('usage falls back when missing, non-array, or empty/unknown', () => {
+  const fallback = [ImageUsage.Emoticon, ImageUsage.Sticker];
+  assert.deepEqual(reader({}).usage, fallback);
+  assert.deepEqual(reader({ usage: 'emoticon' } as unknown as PackMeta).usage, fallback);
+  assert.deepEqual(reader({ usage: [] }).usage, fallback);
+  assert.deepEqual(reader({ usage: ['bogus'] as unknown as ImageUsage[] }).usage, fallback);
+});
+
+test('usage filters to only known values', () => {
+  assert.deepEqual(reader({ usage: [ImageUsage.Emoticon] }).usage, [ImageUsage.Emoticon]);
+  assert.deepEqual(reader({ usage: [ImageUsage.Sticker] }).usage, [ImageUsage.Sticker]);
+  assert.deepEqual(
+    reader({
+      usage: [ImageUsage.Emoticon, 'bogus', ImageUsage.Sticker] as unknown as ImageUsage[],
+    }).usage,
+    [ImageUsage.Emoticon, ImageUsage.Sticker],
+  );
+});
+
+test('content returns the original meta object', () => {
+  const meta: PackMeta = { display_name: 'Cats', usage: [ImageUsage.Emoticon] };
+  assert.equal(reader(meta).content, meta);
+});
diff --git a/src/app/plugins/custom-emoji/utils.test.ts b/src/app/plugins/custom-emoji/utils.test.ts
new file mode 100644
index 000000000..b9cbb8689
--- /dev/null
+++ b/src/app/plugins/custom-emoji/utils.test.ts
@@ -0,0 +1,77 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { MatrixEvent } from 'matrix-js-sdk';
+import { packAddressEqual, imageUsageEqual, packMetaEqual, makeImagePacks } from './utils';
+import { PackAddress } from './PackAddress';
+import { PackMetaReader } from './PackMetaReader';
+import { ImageUsage, PackContent, PackMeta } from './types';
+
+test('packAddressEqual handles undefined and value equality', () => {
+  assert.equal(packAddressEqual(undefined, undefined), true);
+  assert.equal(packAddressEqual(new PackAddress('!r', 'k'), undefined), false);
+  assert.equal(packAddressEqual(undefined, new PackAddress('!r', 'k')), false);
+  assert.equal(packAddressEqual(new PackAddress('!r', 'k'), new PackAddress('!r', 'k')), true);
+  assert.equal(packAddressEqual(new PackAddress('!r', 'k'), new PackAddress('!r', 'j')), false);
+  assert.equal(packAddressEqual(new PackAddress('!r', 'k'), new PackAddress('!s', 'k')), false);
+});
+
+test('imageUsageEqual compares set membership and length', () => {
+  assert.equal(imageUsageEqual([], []), true);
+  assert.equal(imageUsageEqual([ImageUsage.Emoticon], [ImageUsage.Emoticon]), true);
+  assert.equal(
+    imageUsageEqual(
+      [ImageUsage.Emoticon, ImageUsage.Sticker],
+      [ImageUsage.Sticker, ImageUsage.Emoticon],
+    ),
+    true,
+  );
+  assert.equal(imageUsageEqual([ImageUsage.Emoticon], [ImageUsage.Sticker]), false);
+  assert.equal(
+    imageUsageEqual([ImageUsage.Emoticon], [ImageUsage.Emoticon, ImageUsage.Sticker]),
+    false,
+  );
+});
+
+const meta = (m: PackMeta) => new PackMetaReader(m);
+
+test('packMetaEqual compares name, avatar, attribution and usage', () => {
+  assert.equal(packMetaEqual(meta({ display_name: 'A' }), meta({ display_name: 'A' })), true);
+  assert.equal(packMetaEqual(meta({ display_name: 'A' }), meta({ display_name: 'B' })), false);
+  assert.equal(packMetaEqual(meta({ avatar_url: 'u' }), meta({ avatar_url: 'v' })), false);
+  assert.equal(packMetaEqual(meta({ attribution: 'x' }), meta({ attribution: 'y' })), false);
+  // both fall back to default usage => equal
+  assert.equal(packMetaEqual(meta({}), meta({})), true);
+  assert.equal(
+    packMetaEqual(meta({ usage: [ImageUsage.Emoticon] }), meta({ usage: [ImageUsage.Sticker] })),
+    false,
+  );
+});
+
+const eventStub = (id: string | undefined, content: PackContent = {}): MatrixEvent =>
+  ({
+    getId: () => id,
+    getRoomId: () => '!room:server',
+    getStateKey: () => 'state-key',
+    getContent: () => content,
+  }) as unknown as MatrixEvent;
+
+test('makeImagePacks builds packs and skips events without an id', () => {
+  const events = [
+    eventStub('$1', { pack: { display_name: 'One' } }),
+    eventStub(undefined, { pack: { display_name: 'Skip' } }),
+    eventStub('$2', { images: { cat: { url: 'mxc://x/cat' } } }),
+  ];
+  const packs = makeImagePacks(events);
+
+  assert.equal(packs.length, 2);
+  assert.equal(packs[0].id, '$1');
+  assert.equal(packs[0].meta.name, 'One');
+  assert.equal(packs[0].address?.roomId, '!room:server');
+  assert.equal(packs[0].address?.stateKey, 'state-key');
+  assert.equal(packs[1].id, '$2');
+  assert.equal(packs[1].images.collection.get('cat')?.url, 'mxc://x/cat');
+});
+
+test('makeImagePacks returns empty for empty input', () => {
+  assert.deepEqual(makeImagePacks([]), []);
+});
diff --git a/src/app/plugins/markdown/block/parser.test.ts b/src/app/plugins/markdown/block/parser.test.ts
new file mode 100644
index 000000000..6a43d260d
--- /dev/null
+++ b/src/app/plugins/markdown/block/parser.test.ts
@@ -0,0 +1,112 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { parseBlockMD } from './parser';
+import { parseInlineMD } from '../inline/parser';
+
+test('empty string is returned unchanged', () => {
+  assert.equal(parseBlockMD('', parseInlineMD), '');
+});
+
+test('plain single line is returned unchanged', () => {
+  assert.equal(parseBlockMD('hello', parseInlineMD), 'hello');
+});
+
+test('heading levels', () => {
+  assert.equal(parseBlockMD('# Heading', parseInlineMD), '<h1 data-md="#">Heading</h1>');
+  assert.equal(parseBlockMD('### Three', parseInlineMD), '<h3 data-md="###">Three</h3>');
+});
+
+test('heading requires a space after the hashes', () => {
+  // no space => not a heading, falls through to plain text
+  assert.equal(parseBlockMD('#nospace', parseInlineMD), '#nospace');
+});
+
+test('inline markdown inside a heading is parsed', () => {
+  assert.equal(
+    parseBlockMD('# **b**', parseInlineMD),
+    '<h1 data-md="#"><strong data-md="**">b</strong></h1>',
+  );
+});
+
+test('heading without a parseInline function keeps the raw text', () => {
+  assert.equal(parseBlockMD('# Heading', undefined), '<h1 data-md="#">Heading</h1>');
+});
+
+test('fenced code block without info string', () => {
+  assert.equal(
+    parseBlockMD('```\ncode\n```', parseInlineMD),
+    '<pre data-md="```"><code>code\n</code></pre>',
+  );
+});
+
+test('fenced code block with a language', () => {
+  assert.equal(
+    parseBlockMD('```js\ncode\n```', parseInlineMD),
+    '<pre data-md="```"><code class="language-js">code\n</code></pre>',
+  );
+});
+
+test('fenced code block with a filename adds language and data-label', () => {
+  assert.equal(
+    parseBlockMD('```example.json\ncode\n```', parseInlineMD),
+    '<pre data-md="```"><code class="language-json" data-label="example.json">code\n</code></pre>',
+  );
+});
+
+test('blockquote single line', () => {
+  assert.equal(
+    parseBlockMD('> quote', parseInlineMD),
+    '<blockquote data-md=">">quote<br/></blockquote>',
+  );
+});
+
+test('blockquote multiple lines', () => {
+  assert.equal(
+    parseBlockMD('> a\n> b', parseInlineMD),
+    '<blockquote data-md=">">a<br/>b<br/></blockquote>',
+  );
+});
+
+test('unordered list', () => {
+  assert.equal(parseBlockMD('* item', parseInlineMD), '<ul data-md="*"><li><p>item</p></li></ul>');
+});
+
+test('ordered list', () => {
+  assert.equal(
+    parseBlockMD('1. item', parseInlineMD),
+    '<ol data-md="1" start="1"><li><p>item</p></li></ol>',
+  );
+});
+
+test('list with multiple items', () => {
+  assert.equal(
+    parseBlockMD('* a\n* b', parseInlineMD),
+    '<ul data-md="*"><li><p>a</p></li><li><p>b</p></li></ul>',
+  );
+});
+
+test('nested list opens a child list', () => {
+  assert.equal(
+    parseBlockMD('* a\n  * b', parseInlineMD),
+    '<ul data-md="*"><li><p>a</p><ul data-md="*"><li><p>b</p></li></ul></ul>',
+  );
+});
+
+test('inline markdown inside list items is parsed', () => {
+  assert.equal(
+    parseBlockMD('1. **b**', parseInlineMD),
+    '<ol data-md="1" start="1"><li><p><strong data-md="**">b</strong></p></li></ol>',
+  );
+});
+
+test('newlines are preserved as <br/>', () => {
+  assert.equal(parseBlockMD('line1\nline2', parseInlineMD), 'line1<br/>line2');
+});
+
+test('empty lines are preserved as <br/>', () => {
+  assert.equal(parseBlockMD('a\n\nb', parseInlineMD), 'a<br/><br/>b');
+});
+
+test('escaped block sequence is unescaped and not treated as a block', () => {
+  assert.equal(parseBlockMD('\\# not heading', parseInlineMD), '# not heading');
+});
diff --git a/src/app/plugins/markdown/inline/parser.test.ts b/src/app/plugins/markdown/inline/parser.test.ts
new file mode 100644
index 000000000..f0de1fbbb
--- /dev/null
+++ b/src/app/plugins/markdown/inline/parser.test.ts
@@ -0,0 +1,102 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { parseInlineMD } from './parser';
+
+test('empty string is returned unchanged', () => {
+  assert.equal(parseInlineMD(''), '');
+});
+
+test('plain text without markdown is returned unchanged', () => {
+  assert.equal(parseInlineMD('hello world'), 'hello world');
+});
+
+test('bold', () => {
+  assert.equal(parseInlineMD('**bold**'), '<strong data-md="**">bold</strong>');
+});
+
+test('italic with asterisk', () => {
+  assert.equal(parseInlineMD('*italic*'), '<i data-md="*">italic</i>');
+});
+
+test('italic with underscore', () => {
+  assert.equal(parseInlineMD('_italic_'), '<i data-md="_">italic</i>');
+});
+
+test('underline', () => {
+  assert.equal(parseInlineMD('__under__'), '<u data-md="__">under</u>');
+});
+
+test('strikethrough', () => {
+  assert.equal(parseInlineMD('~~strike~~'), '<s data-md="~~">strike</s>');
+});
+
+test('inline code', () => {
+  assert.equal(parseInlineMD('`code`'), '<code data-md="`">code</code>');
+});
+
+test('inline code does not parse markdown inside it', () => {
+  // code is run before the other rules and does not re-parse its content
+  assert.equal(parseInlineMD('`**bold**`'), '<code data-md="`">**bold**</code>');
+});
+
+test('spoiler', () => {
+  assert.equal(parseInlineMD('||secret||'), '<span data-md="||" data-mx-spoiler>secret</span>');
+});
+
+test('link', () => {
+  assert.equal(
+    parseInlineMD('[alt](https://example.com)'),
+    '<a data-md href="https://example.com">alt</a>',
+  );
+});
+
+test('escaped markdown characters are unescaped to literal text', () => {
+  assert.equal(parseInlineMD('\\*notbold\\*'), '*notbold*');
+  assert.equal(parseInlineMD('a\\_b'), 'a_b');
+});
+
+test('nesting: italic inside bold', () => {
+  assert.equal(
+    parseInlineMD('**bold *italic***'),
+    '<strong data-md="**">bold <i data-md="*">italic</i></strong>',
+  );
+});
+
+test('nesting: bold inside link alt text', () => {
+  assert.equal(
+    parseInlineMD('[**b**](https://e.com)'),
+    '<a data-md href="https://e.com"><strong data-md="**">b</strong></a>',
+  );
+});
+
+test('nesting: bold inside spoiler', () => {
+  assert.equal(
+    parseInlineMD('||**b**||'),
+    '<span data-md="||" data-mx-spoiler><strong data-md="**">b</strong></span>',
+  );
+});
+
+test('adjacent tokens of different types are both parsed', () => {
+  assert.equal(parseInlineMD('**a**_b_'), '<strong data-md="**">a</strong><i data-md="_">b</i>');
+});
+
+test('text surrounding a token is preserved', () => {
+  assert.equal(parseInlineMD('pre **mid** post'), 'pre <strong data-md="**">mid</strong> post');
+});
+
+test('two separate tokens are parsed in their text order', () => {
+  assert.equal(parseInlineMD('*a* **b**'), '<i data-md="*">a</i> <strong data-md="**">b</strong>');
+  assert.equal(parseInlineMD('__a__ _b_'), '<u data-md="__">a</u> <i data-md="_">b</i>');
+});
+
+test('code takes precedence and is resolved before other inline rules', () => {
+  assert.equal(parseInlineMD('`a` *b*'), '<code data-md="`">a</code> <i data-md="*">b</i>');
+});
+
+test('unclosed token is returned as literal text', () => {
+  assert.equal(parseInlineMD('**unclosed'), '**unclosed');
+});
+
+test('markdown characters inside a URL are not parsed (negative lookbehind)', () => {
+  assert.equal(parseInlineMD('https://e.com/*path*'), 'https://e.com/*path*');
+});
diff --git a/src/app/plugins/markdown/inline/runner.test.ts b/src/app/plugins/markdown/inline/runner.test.ts
new file mode 100644
index 000000000..e0c693b74
--- /dev/null
+++ b/src/app/plugins/markdown/inline/runner.test.ts
@@ -0,0 +1,56 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { runInlineRule, runInlineRules } from './runner';
+import { parseInlineMD } from './parser';
+import { BoldRule, ItalicRule1, StrikeRule } from './rules';
+import { InlineMDRule } from './type';
+
+// A trivial rule that wraps the matched token in <X>...</X>.
+const makeRule = (token: string, tag: string): InlineMDRule => ({
+  match: (text) => text.match(new RegExp(token)),
+  html: (parse, match) => `<${tag}>${parse(match[0])}</${tag}>`,
+});
+
+test('runInlineRule applies a matching rule', () => {
+  assert.equal(runInlineRule('**b**', BoldRule, parseInlineMD), '<strong data-md="**">b</strong>');
+});
+
+test('runInlineRule returns undefined when the rule does not match', () => {
+  assert.equal(runInlineRule('plain', BoldRule, parseInlineMD), undefined);
+});
+
+test('runInlineRule recursively parses surrounding text', () => {
+  // bold matches in the middle; text on both sides is re-parsed (here it is plain)
+  assert.equal(
+    runInlineRule('pre **mid** post', BoldRule, parseInlineMD),
+    'pre <strong data-md="**">mid</strong> post',
+  );
+});
+
+test('runInlineRules returns undefined when no rule matches', () => {
+  assert.equal(runInlineRules('plain text', [BoldRule, ItalicRule1], parseInlineMD), undefined);
+});
+
+test('runInlineRules picks the earliest-matching rule regardless of rule order', () => {
+  // italic appears before bold in the text, so italic wins even though Bold is listed first
+  assert.equal(
+    runInlineRules('a *i* **b**', [BoldRule, ItalicRule1], parseInlineMD),
+    'a <i data-md="*">i</i> <strong data-md="**">b</strong>',
+  );
+});
+
+test('runInlineRules breaks index ties by rule order (first listed wins)', () => {
+  // Two synthetic rules both match at index 0; the first in the list wins.
+  const aRule = makeRule('a', 'A');
+  const a2Rule = makeRule('a', 'B');
+  assert.equal(runInlineRules('a', [aRule, a2Rule], parseInlineMD), '<A>a</A>');
+  assert.equal(runInlineRules('a', [a2Rule, aRule], parseInlineMD), '<B>a</B>');
+});
+
+test('runInlineRules earliest index wins even when a later-listed rule matches sooner', () => {
+  // Strike token "~~s~~" is at index 0; bold token is later in the string.
+  assert.equal(
+    runInlineRules('~~s~~ **b**', [BoldRule, StrikeRule], parseInlineMD),
+    '<s data-md="~~">s</s> <strong data-md="**">b</strong>',
+  );
+});
diff --git a/src/app/plugins/markdown/internal/utils.test.ts b/src/app/plugins/markdown/internal/utils.test.ts
new file mode 100644
index 000000000..38cbd3268
--- /dev/null
+++ b/src/app/plugins/markdown/internal/utils.test.ts
@@ -0,0 +1,74 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { beforeMatch, afterMatch, replaceMatch } from './utils';
+
+test('beforeMatch returns the slice before the match', () => {
+  const match = 'abXYcd'.match(/XY/)!;
+  assert.equal(beforeMatch('abXYcd', match), 'ab');
+});
+
+test('beforeMatch is empty when the match is at the start', () => {
+  const match = 'XYcd'.match(/XY/)!;
+  assert.equal(beforeMatch('XYcd', match), '');
+});
+
+test('beforeMatch on a match without an index treats index as undefined', () => {
+  // text.slice(0, undefined) returns the whole string
+  const fakeMatch = ['X'] as unknown as RegExpMatchArray;
+  assert.equal(beforeMatch('Xabc', fakeMatch), 'Xabc');
+});
+
+test('afterMatch returns the slice after the match', () => {
+  const match = 'abXYcd'.match(/XY/)!;
+  assert.equal(afterMatch('abXYcd', match), 'cd');
+});
+
+test('afterMatch is empty when the match runs to the end', () => {
+  const match = 'abXY'.match(/XY/)!;
+  assert.equal(afterMatch('abXY', match), '');
+});
+
+test('afterMatch handles a match at the start', () => {
+  const match = 'XYcd'.match(/XY/)!;
+  assert.equal(afterMatch('XYcd', match), 'cd');
+});
+
+test('afterMatch falls back to index 0 when match.index is missing', () => {
+  // (undefined ?? 0) + match[0].length === 1, so it slices off the first char
+  const fakeMatch = ['X'] as unknown as RegExpMatchArray;
+  assert.equal(afterMatch('Xabc', fakeMatch), 'abc');
+});
+
+test('replaceMatch splices content between processed before/after parts', () => {
+  const match = 'abXYcd'.match(/XY/)!;
+  assert.deepEqual(
+    replaceMatch('abXYcd', match, '<R>', (t) => [t]),
+    ['ab', '<R>', 'cd'],
+  );
+});
+
+test('replaceMatch applies processPart to the surrounding text', () => {
+  const match = 'abXYcd'.match(/XY/)!;
+  assert.deepEqual(
+    replaceMatch('abXYcd', match, '<R>', (t) => [t.toUpperCase()]),
+    ['AB', '<R>', 'CD'],
+  );
+});
+
+test('replaceMatch keeps empty surrounding parts produced by processPart', () => {
+  const match = 'XY'.match(/XY/)!;
+  // empty before and after still flow through processPart
+  assert.deepEqual(
+    replaceMatch('XY', match, '<R>', (t) => [t]),
+    ['', '<R>', ''],
+  );
+});
+
+test('replaceMatch supports non-string content types', () => {
+  const match = 'aXb'.match(/X/)!;
+  const node = { type: 'node' };
+  assert.deepEqual(
+    replaceMatch('aXb', match, node, (t) => [t]),
+    ['a', node, 'b'],
+  );
+});
diff --git a/src/app/plugins/recent-emoji.test.ts b/src/app/plugins/recent-emoji.test.ts
new file mode 100644
index 000000000..c23f99a6b
--- /dev/null
+++ b/src/app/plugins/recent-emoji.test.ts
@@ -0,0 +1,114 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { MatrixClient, MatrixEvent } from 'matrix-js-sdk';
+import { addRecentEmoji, getRecentEmojis, IRecentEmojiContent } from './recent-emoji';
+import { AccountDataEvent } from '../../types/matrix/accountData';
+import { emojis } from './emoji';
+
+// A Map-backed MatrixClient stub supporting get/setAccountData.
+const createMx = () => {
+  const store = new Map<string, unknown>();
+  const mx = {
+    getAccountData: (type: string): MatrixEvent | undefined => {
+      if (!store.has(type)) return undefined;
+      const content = store.get(type);
+      return { getContent: () => content } as unknown as MatrixEvent;
+    },
+    setAccountData: (type: string, content: unknown) => {
+      store.set(type, content);
+      return Promise.resolve({});
+    },
+  };
+  return { mx: mx as unknown as MatrixClient, store };
+};
+
+const getStored = (store: Map<string, unknown>): IRecentEmojiContent['recent_emoji'] =>
+  (store.get(AccountDataEvent.ElementRecentEmoji) as IRecentEmojiContent | undefined)?.recent_emoji;
+
+// Pick two real unicode emojis to drive add->get round trips.
+const u1 = emojis[0].unicode;
+const u2 = emojis[1].unicode;
+
+test('getRecentEmojis returns [] when there is no account data', () => {
+  const { mx } = createMx();
+  assert.deepEqual(getRecentEmojis(mx), []);
+});
+
+test('getRecentEmojis returns [] when content is not an array', () => {
+  const { mx, store } = createMx();
+  store.set(AccountDataEvent.ElementRecentEmoji, { recent_emoji: 'nope' });
+  assert.deepEqual(getRecentEmojis(mx), []);
+});
+
+test('addRecentEmoji creates an entry with count 1', () => {
+  const { mx, store } = createMx();
+  addRecentEmoji(mx, u1);
+  assert.deepEqual(getStored(store), [[u1, 1]]);
+});
+
+test('adding the same emoji again increments its count and keeps it at front', () => {
+  const { mx, store } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u1);
+  assert.deepEqual(getStored(store), [[u1, 2]]);
+});
+
+test('a newly added emoji is promoted to the front', () => {
+  const { mx, store } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u2);
+  assert.deepEqual(getStored(store), [
+    [u2, 1],
+    [u1, 1],
+  ]);
+});
+
+test('re-adding an existing emoji promotes it to front and increments', () => {
+  const { mx, store } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u2);
+  addRecentEmoji(mx, u1);
+  assert.deepEqual(getStored(store), [
+    [u1, 2],
+    [u2, 1],
+  ]);
+});
+
+test('list is capped at 100 entries', () => {
+  const { mx, store } = createMx();
+  for (let i = 0; i < 120; i += 1) {
+    addRecentEmoji(mx, `:emoji-${i}:`);
+  }
+  const stored = getStored(store)!;
+  assert.equal(stored.length, 100);
+  // most recently added is at the front
+  assert.equal(stored[0][0], ':emoji-119:');
+});
+
+test('getRecentEmojis resolves stored unicodes to known emoji objects', () => {
+  const { mx } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u2);
+  const recent = getRecentEmojis(mx);
+  assert.equal(recent.length, 2);
+  assert.equal(recent[0].unicode, u2);
+  assert.equal(recent[1].unicode, u1);
+});
+
+test('getRecentEmojis skips unicodes with no matching emoji definition', () => {
+  const { mx } = createMx();
+  addRecentEmoji(mx, ':not-a-real-emoji:');
+  addRecentEmoji(mx, u1);
+  const recent = getRecentEmojis(mx);
+  assert.equal(recent.length, 1);
+  assert.equal(recent[0].unicode, u1);
+});
+
+test('getRecentEmojis respects the limit argument (slice before resolve)', () => {
+  const { mx } = createMx();
+  addRecentEmoji(mx, u1);
+  addRecentEmoji(mx, u2);
+  const recent = getRecentEmojis(mx, 1);
+  assert.equal(recent.length, 1);
+  assert.equal(recent[0].unicode, u2);
+});