diff --git a/src/tools/eta-calculator/eta-calculator.service.test.ts b/src/tools/eta-calculator/eta-calculator.service.test.ts
new file mode 100644
index 00000000..b4526df6
--- /dev/null
+++ b/src/tools/eta-calculator/eta-calculator.service.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, it } from 'vitest';
+import { formatMsDuration } from './eta-calculator.service';
+
+describe('eta-calculator', () => {
+  describe('formatMsDuration', () => {
+    it('should return an empty string for zero or negative durations', () => {
+      expect(formatMsDuration(0)).toEqual('');
+      expect(formatMsDuration(-1)).toEqual('');
+    });
+
+    it('should format durations shorter than an hour', () => {
+      expect(formatMsDuration(1000)).toEqual('1 second');
+      expect(formatMsDuration(42000)).toEqual('42 seconds');
+      expect(formatMsDuration(3599000)).toEqual('59 minutes 59 seconds');
+    });
+
+    it('should format durations with hours', () => {
+      expect(formatMsDuration(3600000)).toEqual('1 hour');
+      expect(formatMsDuration(3660000)).toEqual('1 hour 1 minute');
+      expect(formatMsDuration(3661000)).toEqual('1 hour 1 minute 1 second');
+      expect(formatMsDuration(5400000)).toEqual('1 hour 30 minutes');
+      expect(formatMsDuration(86399000)).toEqual('23 hours 59 minutes 59 seconds');
+    });
+
+    it('should append the truncated milliseconds when some are left', () => {
+      expect(formatMsDuration(1500)).toEqual('1 second 500 ms');
+      expect(formatMsDuration(3661500)).toEqual('1 hour 1 minute 1 second 500 ms');
+      expect(formatMsDuration(1500.9)).toEqual('1 second 500 ms');
+    });
+  });
+});