diff --git a/libraries/deno-commons-mod.ts b/libraries/deno-commons-mod.ts
index b6082c9..22d4855 100644
--- a/libraries/deno-commons-mod.ts
+++ b/libraries/deno-commons-mod.ts
@@ -1,3 +1,8 @@
+// Reference:
+// - https://docs.deno.com/runtime/fundamentals/testing/
+
+import {assertEquals} from "jsr:@std/assert";
+
 export function compareVersion(ver1: string, ver2: string): 0 | 1 | -1 {
     if (ver1 === ver2) return 0;
     const ver1Parts = ver1.split(".");
@@ -29,3 +34,15 @@ export function isOn(val: string | undefined): boolean {
 export function isEnvOn(envKey: string): boolean {
     return isOn(Deno.env.get(envKey));
 }
+
+Deno.test("isOn", () => {
+    assertEquals(false, isOn(undefined));
+    assertEquals(false, isOn(""));
+    assertEquals(true, isOn("true"));
+    assertEquals(true, isOn("TRUE"));
+    assertEquals(true, isOn("yes"));
+    assertEquals(true, isOn("YES"));
+    assertEquals(true, isOn("on"));
+    assertEquals(true, isOn("ON"));
+    assertEquals(true, isOn("1"));
+});