diff --git a/.github/workflows/npm-publish.yml b/.github/workflows/npm-publish.yml
index 58bccf2..65a1491 100644
--- a/.github/workflows/npm-publish.yml
+++ b/.github/workflows/npm-publish.yml
@@ -16,7 +16,7 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 22
-      - run: npm cit
+      - run: npm cit --quiet
         timeout-minutes: 5
 
   publish-npm:
diff --git a/.npmignore b/.npmignore
index ed7205a..c253f51 100644
--- a/.npmignore
+++ b/.npmignore
@@ -2,3 +2,4 @@
 
 .prettierrc.json
 .prettierignore
+*.spec.*
diff --git a/index.spec.mjs b/index.spec.mjs
new file mode 100644
index 0000000..06bdf98
--- /dev/null
+++ b/index.spec.mjs
@@ -0,0 +1,127 @@
+import assert from "node:assert/strict";
+import { test, suite, before, after } from "node:test";
+import postTask from "./index.mjs";
+
+suite("postTask", () => {
+	const {
+		queueMicrotask: queueMicrotaskOriginal,
+		scheduler: schedulerOriginal,
+	} = globalThis;
+
+	suite("when neither the scheduler nor queueMicrotask are available", () => {
+		before(() => {
+			delete globalThis.queueMicrotask;
+			delete globalThis.scheduler;
+		});
+
+		after(() => {
+			globalThis.queueMicrotask = queueMicrotaskOriginal;
+			globalThis.scheduler = schedulerOriginal;
+		});
+
+		test("all priorities should call back", (context) => {
+			context.mock.timers.enable(["setTimeout"]);
+
+			const callback = context.mock.fn();
+
+			// Schedule all tasks synchronously: the loops will queue all three
+			// tasks because there is no `await`.
+			postTask(callback, "user-blocking");
+			postTask(callback, "user-visible");
+			postTask(callback, "background");
+
+			assert.equal(callback.mock.calls.length, 0);
+
+			// Allow the minimal tick to pass, which will enable both timeouts
+			// with a 0ms delay to run, and not the third which has a minimum
+			context.mock.timers.tick(0);
+			assert.equal(callback.mock.calls.length, 2);
+
+			// Allow the 150ms delay for the background task to pass.
+			context.mock.timers.tick(150);
+			assert.equal(callback.mock.calls.length, 3);
+		});
+	});
+
+	suite("when `queueMicrotask` is available", () => {
+		before(() => {
+			delete globalThis.scheduler;
+		});
+
+		after(() => {
+			globalThis.queueMicrotask = queueMicrotaskOriginal;
+			globalThis.scheduler = schedulerOriginal;
+		});
+
+		test("all priorities should call back", async (context) => {
+			context.mock.timers.enable(["setTimeout"]);
+
+			const callback = context.mock.fn();
+
+			// Schedule all tasks synchronously: the loops will queue all three
+			// tasks because there is no `await`.
+			postTask(callback, "user-blocking");
+			postTask(callback, "user-visible");
+			postTask(callback, "background");
+
+			assert.equal(callback.mock.calls.length, 0);
+
+			// Await for the resolution of a microtask: giving that control back to
+			// the event loop results in it running _all_ microtasks, including the
+			// queued one for the `"user-blocking"` task.
+			await Promise.resolve();
+			assert.equal(callback.mock.calls.length, 1);
+
+			// Allow the minimal tick to pass, which will enable both timeouts
+			// with a 0ms delay to run, and not the third which has a minimum
+			context.mock.timers.tick(0);
+			assert.equal(callback.mock.calls.length, 2);
+
+			// Allow the 150ms delay for the background task to pass.
+			context.mock.timers.tick(150);
+			assert.equal(callback.mock.calls.length, 3);
+		});
+	});
+
+	suite("when `scheduler` is available", async () => {
+		after(() => {
+			globalThis.scheduler = schedulerOriginal;
+		});
+
+		test("all priorities should be scheduled", async (context) => {
+			// Mock the function which is to be called
+			const mockSchedulerPostTask = context.mock.fn();
+			globalThis.scheduler = { postTask: mockSchedulerPostTask };
+
+			const noop = () => undefined;
+
+			// Schedule all tasks synchronously
+			postTask(noop, "user-blocking");
+			postTask(noop, "user-visible");
+			postTask(noop, "background");
+
+			// Assert that the control flow correctly forwards the tasks:
+			// the callback is handled by the scheduler, so asserting on the callback
+			// would be testing the mock, and not useful.
+			assert.equal(mockSchedulerPostTask.mock.calls.length, 3);
+			assert.deepEqual(mockSchedulerPostTask.mock.calls[0].arguments, [
+				noop,
+				{
+					priority: "user-blocking",
+				},
+			]);
+			assert.deepEqual(mockSchedulerPostTask.mock.calls[1].arguments, [
+				noop,
+				{
+					priority: "user-visible",
+				},
+			]);
+			assert.deepEqual(mockSchedulerPostTask.mock.calls[2].arguments, [
+				noop,
+				{
+					priority: "background",
+				},
+			]);
+		});
+	});
+});
diff --git a/package.json b/package.json
index a315477..00f4bf9 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,8 @@
 		"require": "./index.cjs"
 	},
 	"scripts": {
-		"test": "node --check index.mjs",
+		"pretest": "node --check index.mjs",
+		"test": "node --disable-warning=ExperimentalWarning ./index.spec.mjs",
 		"prepublishOnly": "sed 's/export default/module.exports =/g' ./index.mjs > index.cjs"
 	},
 	"repository": {