From d850d88a3aed4aa59ba6c9044677fe8062a43f1f Mon Sep 17 00:00:00 2001
From: Dmytro Stanchiev <git@dmytros.dev>
Date: Wed, 8 Apr 2026 19:58:03 -0400
Subject: [PATCH] test: add unit tests for extractImageFromClipboard

---
 tests/clipboard-image.test.ts | 168 ++++++++++++++++++++++++++++++++++
 1 file changed, 168 insertions(+)
 create mode 100644 tests/clipboard-image.test.ts

diff --git a/tests/clipboard-image.test.ts b/tests/clipboard-image.test.ts
new file mode 100644
index 0000000..aabbfd9
--- /dev/null
+++ b/tests/clipboard-image.test.ts
@@ -0,0 +1,168 @@
+import { describe, expect, test } from "bun:test";
+import { extractImageFromClipboard } from "@/lib/clipboard-image";
+
+// ---------------------------------------------------------------------------
+// Clipboard image extraction – pure function tests
+//
+// Public interface under test: extractImageFromClipboard(clipboardData)
+// Takes a DataTransfer (or null) and returns the first image File, or null.
+//
+// Two resolution paths (in priority order):
+//   1. clipboardData.files  – browser-normalised FileList, most reliable
+//   2. clipboardData.items  – DataTransferItemList fallback
+//
+// MIME matching uses startsWith("image/") to handle OS-specific variants
+// like "image/x-png" that a strict allowlist would miss.
+// ---------------------------------------------------------------------------
+
+// ─── Fakes ────────────────────────────────────────────────────────────────────
+
+function makeItem(type: string, file: File | null = null): DataTransferItem {
+	return {
+		kind: file ? "file" : "string",
+		type,
+		getAsFile: () => file,
+		getAsString: () => {},
+		webkitGetAsEntry: () => null,
+	} as unknown as DataTransferItem;
+}
+
+function makeItemList(...items: DataTransferItem[]): DataTransferItemList {
+	return {
+		length: items.length,
+		...Object.fromEntries(items.map((item, i) => [i, item])),
+		[Symbol.iterator]: function* () { yield* items; },
+	} as unknown as DataTransferItemList;
+}
+
+function makeFileList(...files: File[]): FileList {
+	return {
+		length: files.length,
+		...Object.fromEntries(files.map((f, i) => [i, f])),
+		item: (i: number) => files[i] ?? null,
+		[Symbol.iterator]: function* () { yield* files; },
+	} as unknown as FileList;
+}
+
+function makeDataTransfer({
+	files = [] as File[],
+	items = [] as DataTransferItem[],
+} = {}): DataTransfer {
+	return {
+		files: makeFileList(...files),
+		items: makeItemList(...items),
+	} as unknown as DataTransfer;
+}
+
+const PNG_FILE  = new File(["png"],  "image.png",  { type: "image/png"  });
+const JPEG_FILE = new File(["jpg"],  "photo.jpg",  { type: "image/jpeg" });
+const WEBP_FILE = new File(["webp"], "img.webp",   { type: "image/webp" });
+const GIF_FILE  = new File(["gif"],  "anim.gif",   { type: "image/gif"  });
+
+// ─── Path 1: files array (primary) ───────────────────────────────────────────
+
+describe("extractImageFromClipboard – files array (primary path)", () => {
+	test("returns PNG from files array", () => {
+		const dt = makeDataTransfer({ files: [PNG_FILE] });
+		expect(extractImageFromClipboard(dt)).toBe(PNG_FILE);
+	});
+
+	test("returns JPEG from files array", () => {
+		const dt = makeDataTransfer({ files: [JPEG_FILE] });
+		expect(extractImageFromClipboard(dt)).toBe(JPEG_FILE);
+	});
+
+	test("returns WebP from files array", () => {
+		const dt = makeDataTransfer({ files: [WEBP_FILE] });
+		expect(extractImageFromClipboard(dt)).toBe(WEBP_FILE);
+	});
+
+	test("returns first image when files array has multiple images", () => {
+		const dt = makeDataTransfer({ files: [PNG_FILE, JPEG_FILE] });
+		expect(extractImageFromClipboard(dt)).toBe(PNG_FILE);
+	});
+
+	test("prefers files array over items when both present", () => {
+		const dt = makeDataTransfer({
+			files: [JPEG_FILE],
+			items: [makeItem("image/png", PNG_FILE)],
+		});
+		// files is primary — JPEG should win
+		expect(extractImageFromClipboard(dt)).toBe(JPEG_FILE);
+	});
+});
+
+// ─── Path 2: items fallback ───────────────────────────────────────────────────
+
+describe("extractImageFromClipboard – items fallback", () => {
+	test("returns PNG from items when files array is empty", () => {
+		const dt = makeDataTransfer({ items: [makeItem("image/png", PNG_FILE)] });
+		expect(extractImageFromClipboard(dt)).toBe(PNG_FILE);
+	});
+
+	test("returns JPEG from items when files array is empty", () => {
+		const dt = makeDataTransfer({ items: [makeItem("image/jpeg", JPEG_FILE)] });
+		expect(extractImageFromClipboard(dt)).toBe(JPEG_FILE);
+	});
+
+	test("skips text items, returns image from items", () => {
+		const dt = makeDataTransfer({
+			items: [makeItem("text/plain", null), makeItem("image/png", PNG_FILE)],
+		});
+		expect(extractImageFromClipboard(dt)).toBe(PNG_FILE);
+	});
+
+	test("returns null when getAsFile() returns null", () => {
+		const dt = makeDataTransfer({ items: [makeItem("image/png", null)] });
+		expect(extractImageFromClipboard(dt)).toBeNull();
+	});
+});
+
+// ─── startsWith("image/") broadening ─────────────────────────────────────────
+
+describe("extractImageFromClipboard – broad image/* MIME matching", () => {
+	test("accepts image/gif (any image/* accepted now)", () => {
+		const dt = makeDataTransfer({ files: [GIF_FILE] });
+		expect(extractImageFromClipboard(dt)).toBe(GIF_FILE);
+	});
+
+	test("accepts image/x-png (Linux-specific variant)", () => {
+		const xpng = new File(["x"], "x.png", { type: "image/x-png" });
+		const dt = makeDataTransfer({ files: [xpng] });
+		expect(extractImageFromClipboard(dt)).toBe(xpng);
+	});
+
+	test("accepts image/bmp", () => {
+		const bmp = new File(["b"], "b.bmp", { type: "image/bmp" });
+		const dt = makeDataTransfer({ files: [bmp] });
+		expect(extractImageFromClipboard(dt)).toBe(bmp);
+	});
+
+	test("rejects text/plain even if misidentified", () => {
+		const fake = new File(["t"], "t.txt", { type: "text/plain" });
+		const dt = makeDataTransfer({ files: [fake] });
+		expect(extractImageFromClipboard(dt)).toBeNull();
+	});
+});
+
+// ─── Null / empty cases ───────────────────────────────────────────────────────
+
+describe("extractImageFromClipboard – null / empty", () => {
+	test("returns null when clipboardData is null", () => {
+		expect(extractImageFromClipboard(null)).toBeNull();
+	});
+
+	test("returns null when clipboardData is undefined", () => {
+		expect(extractImageFromClipboard(undefined)).toBeNull();
+	});
+
+	test("returns null when both files and items are empty", () => {
+		const dt = makeDataTransfer();
+		expect(extractImageFromClipboard(dt)).toBeNull();
+	});
+
+	test("returns null for text-only clipboard", () => {
+		const dt = makeDataTransfer({ items: [makeItem("text/plain", null)] });
+		expect(extractImageFromClipboard(dt)).toBeNull();
+	});
+});