add code

deno.jsonc

@@ -1,5 +1,9 @@
 {
     "fmt": {
         "indentWidth": 4
+    },
+    "tasks": {
+        "check": "deno check main.ts",
+        "test": "deno test"
     }
 }

deno.lock

@@ -0,0 +1,21 @@
+{
+  "version": "3",
+  "packages": {
+    "specifiers": {
+      "jsr:@std/assert": "jsr:@std/assert@1.0.5",
+      "jsr:@std/internal@^1.0.3": "jsr:@std/internal@1.0.3"
+    },
+    "jsr": {
+      "@std/assert@1.0.5": {
+        "integrity": "e37da8e4033490ce613eec4ac1d78dba1faf5b02a3f6c573a28f15365b9b440f",
+        "dependencies": [
+          "jsr:@std/internal@^1.0.3"
+        ]
+      },
+      "@std/internal@1.0.3": {
+        "integrity": "208e9b94a3d5649bd880e9ca38b885ab7651ab5b5303a56ed25de4755fb7b11e"
+      }
+    }
+  },
+  "remote": {}
+}

main.ts

@@ -1 +1,3 @@
-console.log("hello world");
+import { message } from "./message.ts";
+
+console.log(message());

message.ts

@@ -0,0 +1,3 @@
+export function message(): string {
+    return "hello world";
+}

message_test.ts

@@ -0,0 +1,6 @@
+import { assertEquals } from "jsr:@std/assert";
+import { message } from "./message.ts";
+
+Deno.test("message is correct", () => {
+    assertEquals(message(), "hello world");
+});