Enable supplying a commit message template

src/template.test.ts

@@ -0,0 +1,31 @@
+import { renderCommitMessage } from "./template.js";
+import { describe, expect, test } from "vitest";
+
+describe("templating", () => {
+  test("commit message", () => {
+    type TestCase = {
+      template: string;
+      flakeDotLock: string;
+      expected: string;
+    };
+
+    const testCases: TestCase[] = [
+      {
+        template: "Updating lockfile at {{ flake_dot_lock }}",
+        flakeDotLock: "./flake.lock",
+        expected: "Updating lockfile at ./flake.lock",
+      },
+      {
+        template:
+          "Here I go doing some updating of my pristine flake.lock at {{ flake_dot_lock }}",
+        flakeDotLock: "subflake/flake.lock",
+        expected:
+          "Here I go doing some updating of my pristine flake.lock at subflake/flake.lock",
+      },
+    ];
+
+    testCases.forEach(({ template, flakeDotLock, expected }) => {
+      expect(renderCommitMessage(template, flakeDotLock)).toEqual(expected);
+    });
+  });
+});