wip.4

packages/bun-types/test.d.ts

@@ -697,6 +697,40 @@ declare module "bun:test" {
      * Ensures that a specific number of assertions are made
      */
     assertions(neededAssertions: number): void;
+
+    /**
+     * Add a custom snapshot serializer to customize how values are formatted in snapshots.
+     *
+     * @example
+     * class Point {
+     *   constructor(public x: number, public y: number) {}
+     * }
+     *
+     * expect.addSnapshotSerializer({
+     *   test: (val) => val instanceof Point,
+     *   serialize: (val) => `Point(${val.x}, ${val.y})`,
+     * });
+     *
+     * expect(new Point(1, 2)).toMatchInlineSnapshot(`Point(1, 2)`);
+     *
+     * @param serializer The snapshot serializer configuration
+     */
+    addSnapshotSerializer(serializer: {
+      /**
+       * Test function to determine if this serializer should be used for a value
+       */
+      test: (val: any) => boolean;
+      /**
+       * Serialize function to convert the value to a string.
+       * Either `serialize` or `print` must be provided.
+       */
+      serialize?: (val: any) => string;
+      /**
+       * Print function to convert the value to a string (alternative to serialize).
+       * Either `serialize` or `print` must be provided.
+       */
+      print?: (val: any) => string;
+    }): void;
   }
 
   /**

test/js/bun/test/snapshot-serializers.test.ts

@@ -0,0 +1,70 @@
+import { expect, test } from "bun:test";
+
+class Point {
+  constructor(
+    public x: number,
+    public y: number,
+  ) {}
+}
+
+class Color {
+  constructor(public name: string) {}
+}
+
+class Size {
+  constructor(
+    public width: number,
+    public height: number,
+  ) {}
+}
+
+// Add serializers at the top level
+expect.addSnapshotSerializer({
+  test: val => val instanceof Point,
+  serialize: val => `Point(${val.x}, ${val.y})`,
+});
+
+expect.addSnapshotSerializer({
+  test: val => val instanceof Color,
+  serialize: val => `Color[${val.name}]`,
+});
+
+// Add a second Point serializer to test that most recent wins
+expect.addSnapshotSerializer({
+  test: val => val instanceof Point,
+  serialize: val => `OVERRIDE: Point(${val.x}, ${val.y})`,
+});
+
+expect.addSnapshotSerializer({
+  test: val => val instanceof Size,
+  print: val => `Size{${val.width}x${val.height}}`,
+});
+
+test("snapshot serializers work for custom formatting", () => {
+  const color = new Color("red");
+  expect(color).toMatchInlineSnapshot(`Color[red]`);
+});
+
+test("most recently added serializer is used when multiple match", () => {
+  // The second Point serializer should be used (most recent wins)
+  const point = new Point(10, 20);
+  expect(point).toMatchInlineSnapshot(`OVERRIDE: Point(10, 20)`);
+});
+
+test("snapshot serializer with 'print' instead of 'serialize'", () => {
+  const size = new Size(100, 200);
+  expect(size).toMatchInlineSnapshot(`Size{100x200}`);
+});
+
+test("snapshot serializers apply to object fields", () => {
+  const obj = {
+    color: new Color("blue"),
+    size: new Size(640, 480),
+  };
+  expect(obj).toMatchInlineSnapshot(`
+    {
+      "color": Color[blue],
+      "size": Size{640x480},
+    }
+  `);
+});