diff --git a/screen.js b/screen.js
index ed19b64..8b2943f 100644
--- a/screen.js
+++ b/screen.js
@@ -168,6 +168,21 @@ function _smFmt(s) {
     return Math.floor(s / 60) + ':' + String(Math.floor(s % 60)).padStart(2, '0');
 }
 
+// Node-only export hook for tests; browsers fall through to the side-effect
+// IIFE below (poller + playSong/showScreen wrapping).
+if (typeof module !== 'undefined' && module.exports) {
+    module.exports = {
+        _smGetColor, _smFmt, _smCreate, _smRemove, _smUpdate, _smRender,
+        _smOnClick, _smOnWheel,
+        _getState: () => ({ bar: _smBar, sections: _smSections, duration: _smDuration }),
+        _setState(next) {
+            if ('sections' in next) _smSections = next.sections;
+            if ('duration' in next) _smDuration = next.duration;
+            if ('bar' in next) _smBar = next.bar;
+        },
+    };
+} else {
+
 // Side effects: poller + playSong/showScreen wrappers. Consolidated under
 // one idempotency guard so re-evaluation (loader cache miss, hot reload,
 // older core builds without the load-side guard) doesn't start a second
@@ -197,3 +212,5 @@ function _smFmt(s) {
         origShowScreen(id);
     };
 })();
+
+}
diff --git a/tests/screen.test.js b/tests/screen.test.js
new file mode 100644
index 0000000..5e4e4ef
--- /dev/null
+++ b/tests/screen.test.js
@@ -0,0 +1,147 @@
+'use strict';
+// Coverage for pure/DOM-light helpers in screen.js: section color lookup,
+// time formatting, render HTML shape, click/wheel seek math.
+// Runs under the org reusable CI as `node tests/screen.test.js`.
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const path = require('node:path');
+
+function freshPlugin() {
+    global.window = {};
+    global.document = { getElementById: () => null };
+    const file = path.join(__dirname, '..', 'screen.js');
+    delete require.cache[require.resolve(file)];
+    return require(file);
+}
+
+class FakeBar {
+    constructor() {
+        this.innerHTML = '';
+        this.style = {};
+        this._listeners = {};
+        this.left = 0;
+        this.width = 500;
+    }
+    addEventListener(type, fn) { this._listeners[type] = fn; }
+    getBoundingClientRect() { return { left: this.left, width: this.width }; }
+    querySelectorAll() { return []; }
+}
+
+class FakeAudio {
+    constructor() {
+        this.currentTime = 0;
+        this.paused = true;
+        this._listeners = {};
+    }
+    pause() { this.paused = true; }
+    play() { this.paused = false; }
+    addEventListener(type, fn) { this._listeners[type] = fn; }
+    removeEventListener() {}
+}
+
+test('_smGetColor matches by substring, case-insensitively', () => {
+    const mod = freshPlugin();
+    assert.equal(mod._smGetColor('Verse 1'), '#22c55e');
+    assert.equal(mod._smGetColor('CHORUS'), '#eab308');
+    assert.equal(mod._smGetColor('Guitar Solo'), '#ef4444');
+});
+
+test('_smGetColor falls back to default for an unrecognized section name', () => {
+    const mod = freshPlugin();
+    assert.equal(mod._smGetColor('Mystery Section'), '#4b5563');
+});
+
+test('_smFmt formats seconds as m:ss with zero-padded seconds', () => {
+    const mod = freshPlugin();
+    assert.equal(mod._smFmt(0), '0:00');
+    assert.equal(mod._smFmt(65), '1:05');
+    assert.equal(mod._smFmt(600), '10:00');
+});
+
+test('_smRender builds one .sm-block-tagged div per section plus a position marker', () => {
+    const mod = freshPlugin();
+    const bar = new FakeBar();
+    mod._setState({
+        bar,
+        sections: [{ name: 'Intro', time: 0 }, { name: 'Verse 1', time: 10 }],
+        duration: 20,
+    });
+    mod._smRender();
+    assert.equal((bar.innerHTML.match(/sm-block/g) || []).length, 2);
+    assert.ok(bar.innerHTML.includes('id="sm-marker"'));
+    assert.ok(bar.innerHTML.includes('left:0%'));   // Intro starts at 0%
+    assert.ok(bar.innerHTML.includes('left:50%'));  // Verse 1 starts at 10/20
+});
+
+test('_smRender strips a trailing numeric suffix and capitalizes the label', () => {
+    const mod = freshPlugin();
+    const bar = new FakeBar();
+    mod._setState({ bar, sections: [{ name: 'verse2', time: 0 }], duration: 10 });
+    mod._smRender();
+    assert.ok(bar.innerHTML.includes('>Verse<'));
+});
+
+test('_smOnClick seeks to the clicked fraction of the bar', () => {
+    const mod = freshPlugin();
+    const bar = new FakeBar();
+    bar.width = 500;
+    const audio = new FakeAudio();
+    audio.paused = true; // not playing -> seeks immediately, no resume dance
+    mod._setState({ bar, sections: [{ name: 'Intro', time: 0 }], duration: 100 });
+    global.document = { getElementById: (id) => (id === 'audio' ? audio : null) };
+
+    mod._smOnClick({ clientX: 250 }); // 50% across a 500px-wide bar
+    assert.equal(audio.currentTime, 50);
+});
+
+test('_smOnClick pauses, seeks, and resumes playback while playing', () => {
+    const mod = freshPlugin();
+    const bar = new FakeBar();
+    const audio = new FakeAudio();
+    audio.paused = false;
+    mod._setState({ bar, sections: [{ name: 'Intro', time: 0 }], duration: 100 });
+    global.document = { getElementById: (id) => (id === 'audio' ? audio : null) };
+
+    mod._smOnClick({ clientX: 0 });
+    assert.equal(audio.currentTime, 0);
+    assert.equal(audio.paused, true); // paused before the seek
+    audio._listeners.seeked(); // simulate the browser firing 'seeked'
+    assert.equal(audio.paused, false); // resumed
+});
+
+test('_smOnWheel computes a fine-grained seek delta with ctrlKey', () => {
+    const mod = freshPlugin();
+    const audio = new FakeAudio();
+    audio.currentTime = 10;
+    audio.paused = true;
+    mod._setState({ bar: new FakeBar(), sections: [{ name: 'Intro', time: 0 }], duration: 100 });
+    global.document = { getElementById: (id) => (id === 'audio' ? audio : null) };
+
+    let prevented = false;
+    mod._smOnWheel({ deltaY: -1, ctrlKey: true, preventDefault: () => { prevented = true; } });
+    assert.equal(prevented, true);
+    assert.equal(audio.currentTime, 10.1); // scroll up -> forward by 0.1s (ctrl = fine)
+});
+
+test('_smOnWheel without ctrlKey moves a full second and clamps to [0, duration]', () => {
+    const mod = freshPlugin();
+    const audio = new FakeAudio();
+    audio.currentTime = 0;
+    audio.paused = true;
+    mod._setState({ bar: new FakeBar(), sections: [{ name: 'Intro', time: 0 }], duration: 100 });
+    global.document = { getElementById: (id) => (id === 'audio' ? audio : null) };
+
+    mod._smOnWheel({ deltaY: 1, ctrlKey: false, preventDefault: () => {} }); // scroll down -> backward
+    assert.equal(audio.currentTime, 0); // clamped at 0, can't go negative
+});
+
+test('_smOnWheel/_smOnClick are no-ops without a known duration', () => {
+    const mod = freshPlugin();
+    const audio = new FakeAudio();
+    mod._setState({ bar: new FakeBar(), sections: [], duration: 0 });
+    global.document = { getElementById: (id) => (id === 'audio' ? audio : null) };
+
+    mod._smOnClick({ clientX: 100 });
+    mod._smOnWheel({ deltaY: 1, preventDefault: () => {} });
+    assert.equal(audio.currentTime, 0); // untouched
+});