diff --git a/test/into.test.ts b/test/into.test.ts
new file mode 100644
index 0000000..fb3d33b
--- /dev/null
+++ b/test/into.test.ts
@@ -0,0 +1,84 @@
+import { into } from '~/into';
+
+describe(`sync`, () => {
+  test(`works wo/ a function`, () => {
+    const value = into('foo');
+    expect(value).toBe('foo');
+  });
+  test(`works w/ 1 function`, () => {
+    const value = into('foo', (value: string) => value + 'bar');
+    expect(value).toBe('foobar');
+  });
+  test(`works w/ a number of functions`, () => {
+    const value = into(
+      'foo',
+      (value: string) => value + 'bar',
+      (value) => ({ value }),
+      (value) => ({ value: value.value + 'baz' })
+    );
+
+    expect(value).toEqual({ value: 'foobarbaz' });
+  });
+  test(`works w/ intermediary undefined values`, () => {
+    const value = into(
+      'foo',
+      (value: string) => value + 'bar',
+      undefined,
+      (value) => ({ value }),
+      undefined,
+      undefined,
+      (value) => ({ value: value.value + 'baz' }),
+      undefined
+    );
+
+    expect(value).toEqual({ value: 'foobarbaz' });
+  });
+});
+
+describe(`async`, () => {
+  test(`returns a promise`, () => {
+    const promise = into.async('foo');
+
+    expect(promise).toBeInstanceOf(Promise);
+  });
+  test(`works wo/ a function`, async () => {
+    const promise = into.async('foo');
+
+    await expect(promise).resolves.toBe('foo');
+  });
+  test(`works w/ 1 sync function`, async () => {
+    const promise = into.async('foo', (value: string) => value + 'bar');
+
+    await expect(promise).resolves.toBe('foobar');
+  });
+  test(`works w/ 1 async function`, async () => {
+    const promise = into.async('foo', async (value: string) => value + 'bar');
+
+    await expect(promise).resolves.toBe('foobar');
+  });
+  test(`works w/ a number of functions`, async () => {
+    const promise = into.async(
+      'foo',
+      async (value: string) => value + 'bar',
+      (value) => ({ value }),
+      async (value) => ({ value: value.value + 'baz' })
+    );
+
+    await expect(promise).resolves.toEqual({ value: 'foobarbaz' });
+  });
+  test(`works w/ intermediary undefined values`, async () => {
+    const promise = into.async(
+      'foo',
+      undefined,
+      async (value: string) => value + 'bar',
+      undefined,
+      (value) => ({ value }),
+      undefined,
+      undefined,
+      async (value) => ({ value: value.value + 'baz' }),
+      undefined
+    );
+
+    await expect(promise).resolves.toEqual({ value: 'foobarbaz' });
+  });
+});