3 files changed, 34 insertions, 18 deletions
diff --git a/src/serializers/to_json.ts b/src/serializers/to_json.ts
index 9f7b59b..f915a88 100644
--- a/src/serializers/to_json.ts
+++ b/src/serializers/to_json.ts
@@ -1,7 +1,7 @@
-import {Matter, Serializer} from '../flatmatter.ts';
+import type { Matter, Serializer } from "../flatmatter.ts";
 
 export default class ToJson implements Serializer {
-    serialize(parsedConfig: Matter): string {
-        return JSON.stringify(parsedConfig);
-    }
-}
-\ No newline at end of file
+  serialize(parsedConfig: Matter): string {
+    return JSON.stringify(parsedConfig);
+  }
+}
diff --git a/src/serializers/to_object.test.ts b/src/serializers/to_object.test.ts
index 98b165a..9f13987 100644
--- a/src/serializers/to_object.test.ts
+++ b/src/serializers/to_object.test.ts
@@ -1,13 +1,12 @@
-import { assertEquals } from "jsr:@std/assert";
-import FlatMatter from "../flatmatter.ts";
+import FlatMatter, {type FlatMatterFn} from "../flatmatter.ts";
 import ToObject from "./to_object.ts";
 
-Deno.test("Single-level configuration", () => {
+test("Single-level configuration", () => {
   const fm = new FlatMatter(
-    'a: true\nb: false\nc: 1\nd: 12.5\nf: "some string"',
+    'a: true\nb: false\nc: 1\nd: 12.5\nf: "some string"'
   );
 
-  assertEquals(fm.serialize(new ToObject()), {
+  expect(fm.serialize(new ToObject())).toStrictEqual({
     a: true,
     b: false,
     c: 1,
@@ -16,12 +15,12 @@ Deno.test("Single-level configuration", () => {
   });
 });
 
-Deno.test("Two-level configuration", () => {
+test("Two-level configuration", () => {
   const fm = new FlatMatter(
-    'a.a: true\nb.b: false\nc.c: 1\nd.d: 12.5\nf.f: "some string"',
+    'a.a: true\nb.b: false\nc.c: 1\nd.d: 12.5\nf.f: "some string"'
   );
 
-  assertEquals(fm.serialize(new ToObject()), {
+  expect(fm.serialize(new ToObject())).toStrictEqual({
     a: {
       a: true,
     },
@@ -39,3 +38,20 @@ Deno.test("Two-level configuration", () => {
     },
   });
 });
+
+test("Simple function usage", () => {
+  class ToUpper implements FlatMatterFn {
+    name = "to-upper";
+
+    compute(input: string): unknown {
+      return input.toUpperCase();
+    }
+  }
+
+  const fm = new FlatMatter('a: (to-upper "value")', [new ToUpper()]);
+  const config = fm.serialize(new ToObject());
+
+  expect(config).toStrictEqual({
+    a: "VALUE",
+  });
+});
diff --git a/src/serializers/to_object.ts b/src/serializers/to_object.ts
index eb21d2f..1b07144 100644
--- a/src/serializers/to_object.ts
+++ b/src/serializers/to_object.ts
@@ -1,7 +1,7 @@
-import {Matter, Serializer} from '../flatmatter.ts';
+import type { Matter, Serializer } from "../flatmatter.ts";
 
 export default class ToObject implements Serializer {
-    serialize(parsedConfig: Matter): Matter {
-        return parsedConfig;
-    }
-}
-\ No newline at end of file
+  serialize(parsedConfig: Matter): Matter {
+    return parsedConfig;
+  }
+}