diff --git a/tests/assets.test.mjs b/tests/assets.test.mjs
index a93e274..78b24ca 100644
--- a/tests/assets.test.mjs
+++ b/tests/assets.test.mjs
@@ -7,6 +7,8 @@ import rightControls from '../src/assets/controller/right-controls.js';
 import cannonRoundel from '../src/assets/controller/cannon-roundel.js';
 import helmFrame from '../src/assets/controller/helm-frame.js';
 import helmKnob from '../src/assets/controller/helm-knob.js';
+import playerHealth from '../src/assets/controller/player-health.js';
+import enemyHealth from '../src/assets/controller/enemy-health.js';
 
 const assets = {
   topHud,
@@ -15,6 +17,8 @@ const assets = {
   cannonRoundel,
   helmFrame,
   helmKnob,
+  playerHealth,
+  enemyHealth,
 };
 
 const decodeWebP = (name, dataUrl) => {
@@ -40,3 +44,20 @@ for (const [name, dataUrl] of Object.entries(assets)) {
     decodeWebP(name, dataUrl);
   });
 }
+
+const alphaAssets = {
+  topHud,
+  playerHealth,
+  enemyHealth,
+};
+
+for (const [name, dataUrl] of Object.entries(alphaAssets)) {
+  test(`${name} carries WebP transparency data`, () => {
+    const match = /^data:image\/webp;base64,([A-Za-z0-9+/=]+)$/.exec(dataUrl);
+    assert.ok(match, `${name} must be a WebP data URL`);
+    const bytes = Buffer.from(match[1], 'base64');
+    const hasAlphaChunk = bytes.includes(Buffer.from('ALPH'));
+    const usesLosslessWebP = bytes.includes(Buffer.from('VP8L'));
+    assert.ok(hasAlphaChunk || usesLosslessWebP, `${name} should preserve transparent background data`);
+  });
+}