Initial @inngest/test package (#704)

## Summary
<!-- Succinctly describe your change, providing context, what you've
changed, and why. -->

The initial bare-bones release of `@inngest/test` based on the RFC at
inngest/inngest#1680 following the preliminary changes to open up the
execution APIs in #688.

To see how to use the library in its current state, see
[`README.md`](https://github.com/inngest/inngest-js/tree/feat/inngest-test/packages/test).

## Checklist
<!-- Tick these items off as you progress. -->
<!-- If an item isn't applicable, ideally please strikeout the item by
wrapping it in "~~"" and suffix it with "N/A My reason for skipping
this." -->
<!-- e.g. "- [ ] ~~Added tests~~ N/A Only touches docs" -->

- [ ] ~Added a [docs PR](https://github.com/inngest/website) that
references this PR~ N/A Package has a readme - will follow up with docs
- [ ] ~Added unit/integration tests~ N/A Package still `0.` - will pad
out utests later
- [x] Added changesets if applicable

## Related
<!-- A space for any related links, issues, or PRs. -->
<!-- Linear issues are autolinked. -->
<!-- e.g. - INN-123 -->
<!-- GitHub issues/PRs can be linked using shorthand. -->
<!-- e.g. "- inngest/inngest#123" -->
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links.-->
- Follows #688
- Based on RFC at inngest/inngest#1680
- Python: inngest/inngest-py#152

.changeset/violet-bikes-study.md

@@ -0,0 +1,5 @@
+---
+"@inngest/test": minor
+---
+
+Refactor `@inngest/test` to have a much simpler public API

packages/test/.gitignore

@@ -1,2 +1,3 @@
 dist
 node_modules
+inngest-test.tgz

packages/test/README.md

@@ -1,5 +1,315 @@
 # @inngest/test
 
-- [ ] TODO Make Inngest a peer dep once package changes are shipped
-- [ ] TODO Re-add release scripts
-- [ ] TODO Copy `CHANGELOG.md`
+This package helps you test your Inngest functions with Jest-compatible mocking,
+allowing you to mock function state, step tooling, and inputs. Jest
+compatibility means we aim for compatibility with all major testing frameworks,
+runtimes, and libraries:
+
+- `jest`
+- `vitest`
+- `bun:test` (Bun)
+- `@std/expect` (Deno)
+- `chai`/`expect`
+
+## Table of contents
+
+- [Installation](#installation)
+- [Running tests](#running-tests)
+  - [Running an entire function](#running-tests)
+  - [Running an individual step](#running-an-individual-step)
+- [Assertions](#assertions)
+  - [Function/step output](#assertions)
+  - [Function input](#assertions)
+  - [Step state](#assertions)
+- [Mocking](#mocking)
+  - [Events](#event-data)
+  - [Steps](#step-data)
+  - [Modules and imports](#modules-and-imports)
+  - [Custom](#custom)
+- [TODO](#known-issues--todo)
+
+## Installation
+
+This package requires `inngest@>=3.22.12`.
+
+```
+npm install -D @inngest/test
+```
+
+## Running tests
+
+Use whichever supported testing framework; `@inngest/test` is unopinionated
+about how your tests are run. We'll demonstrate here using `jest`.
+
+We import `InngestTestEngine` and our target function, `helloWorld`, and create
+a new `InngestTestEngine` instance.
+
+```ts
+import { InngestTestEngine } from "@inngest/test";
+import { helloWorld } from "./helloWorld";
+
+describe("helloWorld function", () => {
+  const t = new InngestTestEngine({
+    function: helloWorld,
+  });
+});
+```
+
+Within that, we'll add a new test using the primary API,
+`t.execute()`:
+
+```ts
+test("returns a greeting", async () => {
+  const { result } = await t.execute();
+  expect(result).toEqual("Hello World!");
+});
+```
+
+This will run the entire function (steps and all) to completion, then return the
+response from the function, where we assert that it was the string `"Hello
+World!"`.
+
+An error
+
+### Running an individual step
+
+`t.executeStep()` can be used to run the function until a particular step has
+been executed. This is useful to test a single step within a function or to see
+that a non-runnable step such as `step.waitForEvent()` has been registered with
+the correct options.
+
+```ts
+test("runs the price calculations", async () => {
+  const { result } = await t.executeStep("calculate-price");
+  expect(result).toEqual(123);
+});
+```
+
+Assertions can also be made on steps in any part of a run, regardless of if
+that's the checkpoint we've waited for. See [Assertions -> State](#assertions).
+
+## Assertions
+
+Inngest adds like Jest-compatible mocks by default that can help you assert
+function and step input and output. You can assert:
+
+- Function input
+- Function output
+- Step output
+- Step tool usage
+
+All of these values are returned from both `t.execute()` and `t.executeStep()`;
+we'll only show one for simplicity here.
+
+The `result` is returned, which is the output of the run or step:
+
+```ts
+const { result } = await t.execute();
+expect(result).toEqual("Hello World!");
+```
+
+`ctx` is the input used for the function run. This can be used to assert outputs
+that are based on input data such as `event` or `runId`:
+
+```ts
+const { ctx, result } = await t.execute();
+expect(result).toEqual(`Run ID was: "${ctx.runId}"`);
+```
+
+> [!NOTE]
+> The tests also run middleware, so you can test that middleware inputs are also
+> being used correctly.
+
+The step tooling at `ctx.step` are Jest-compatible spy functions, so you can use
+them to assert that they've been called and used correctly:
+
+```ts
+const { ctx } = await t.execute();
+expect(ctx.step.run).toHaveBeenCalledWith("my-step", expect.any(Function));
+```
+
+`state` is also returned, which is a view into the outputs of all of the steps
+in the run. This allows you to test each individual step output for any given
+input:
+
+```ts
+const { state } = await t.execute();
+expect(state["my-step"]).resolves.toEqual("some successful output");
+expect(state["dangerous-step"]).rejects.toThrowError("something failed");
+```
+
+## Mocking
+
+Some mocking is done automatically by `@inngest/test`, but can be overwritten if
+needed.
+
+All mocks (detailed below) can be specified either when creating an `InngestTestEngine` instance
+or for each individual execution:
+
+```ts
+// Set the events for every execution
+const t = new InngestTestEngine({
+  function: helloWorld,
+  // mocks here
+});
+
+// Or for just one, which will overwrite any current event mocks
+t.execute({
+  // mocks here
+});
+
+t.executeStep("my-step", {
+  // mocks here
+})
+```
+
+You can also clone an existing `InngestTestEngine` instance to encourage re-use
+of complex mocks:
+
+```ts
+// Make a direct clone, which includes any mocks
+const otherT = t.clone();
+
+// Provide some more mocks in addition to any existing ones
+const anotherT = t.clone({
+  // mocks here
+});
+```
+
+For simplicity, the following examples will show usage of
+`t.execute()`, but the mocks can be placed in any of these locations.
+
+### Event data
+
+The incoming event data can be mocked. They are always specified as an array of
+events to allow also mocking batches.
+
+```ts
+t.execute({
+  events: [{ name: "demo/event.sent", data: { message: "Hi!" } }],
+});
+```
+
+If no event mocks are given at all (or `events: undefined` is explicitly set),
+an `inngest/function.invoked` event will be mocked for you.
+
+### Step data
+
+Mocking step data can help you model different paths and situations within your
+function. To do so, any step can be mocked by providing the `steps` option.
+
+Here we mock two steps, one that will run successfully and another that will
+model a failure and throw an error.
+
+```ts
+t.execute({
+  steps: [
+    {
+      id: "successful-step",
+      handler() {
+        return "We did it!";
+      },
+    },
+    {
+      id: "dangerous-step",
+      handler() {
+        throw new Error("Oh no!");
+      },
+    },
+  ],
+});
+```
+
+These handlers will run lazily when they are found during a function's
+execution. This means you can write complex mocks that respond to other
+information:
+
+```ts
+let message = "";
+
+t.execute({
+  steps: [
+    {
+      id: "build-greeting",
+      handler() {
+        message = "Hello, ";
+        return message;
+      },
+    },
+    {
+      id: "build-name",
+      handler() {
+        return message + " World!";
+      },
+    },
+  ],
+});
+```
+
+> [!NOTE]
+> We'll later add `ctx` and `state` to the input of `handler`, meaning you'll
+> get much easier access to existing state and function input in order to
+> provide more accurate mocks.
+
+### Modules and imports
+
+Any mocking of modules or imports outside of Inngest which your functions may
+rely on should be done outside of Inngest with the testing framework you're
+using. For convenience, here are some links to the major supported frameworks
+and their guidance for mocking imports:
+
+- [`jest`](https://jestjs.io/docs/mock-functions#mocking-modules)
+- [`vitest`](https://vitest.dev/guide/mocking#modules)
+- [`bun:test` (Bun)](https://bun.sh/docs/test/mocks#module-mocks-with-mock-module)
+- [`@std/testing` (Deno)](https://jsr.io/@std/testing/doc/mock/~)
+
+### Custom
+
+While the package performs some basic mocks of the input object to a function in
+order to spy on `ctx.step.*`, you can provide your own mocks for the function
+input to do whatever you want with.
+
+When instantiating a new `InngestTestEngine` or starting an execution, provide a
+`transformCtx` function that will add these mocks every time the function is
+run:
+
+```ts
+const t = new InngestTestEngine({
+  function: helloWorld,
+  transformCtx: (ctx) => {
+    return {
+      ...ctx,
+      event: someCustomThing,
+    };
+  },
+});
+```
+
+If you wish to still add the automatic spies to `ctx.step.*`, you can import and
+use the automatic transforms as part of your own:
+
+```ts
+import { InngestTestEngine, mockCtx } from "@inngest/test";
+
+const t = new InngestTestEngine({
+  function: helloWorld,
+  transformCtx: (ctx) => {
+    return {
+      ...mockCtx(ctx),
+      event: someCustomThing,
+    };
+  },
+});
+```
+
+## Known issues / TODO
+
+- There are currently no retries modelled; any step or function that fails once
+  will fail permanently
+- `onFailure` handlers are not run automatically
+- Mocked step outputs do not model the JSON (de)serialization process yet, so
+  some typing may be off (e.g. `Date`)
+- You cannot specify any `reqArgs` yet, which could affect some middleware usage
+  that relies on a particular serve handler being used
+- Calling `inngest.send()` within a function is not yet automatically mocked, likely
+  resulting in an error

packages/test/package.json

@@ -9,10 +9,14 @@
   },
   "scripts": {
     "test": "jest",
+    "build": "pnpm run build:clean && pnpm run build:tsc && pnpm run build:copy",
     "build:clean": "rm -rf ./dist",
     "build:tsc": "tsc --project tsconfig.build.json",
-    "build:copy": "cp package.json LICENSE.md README.md dist",
-    "pack": "pnpm run build && yarn pack --verbose --frozen-lockfile --filename inngest-test.tgz --cwd dist"
+    "build:copy": "cp package.json LICENSE.md README.md CHANGELOG.md dist",
+    "pack": "pnpm run build && yarn pack --verbose --frozen-lockfile --filename inngest-test.tgz --cwd dist",
+    "postversion": "pnpm run build && pnpm run build:copy",
+    "release": "DIST_DIR=dist node ../../scripts/release/publish.js && pnpm dlx jsr publish --allow-slow-types --allow-dirty",
+    "release:version": "node ../../scripts/release/jsrVersion.js"
   },
   "exports": {
     ".": {
@@ -34,10 +38,14 @@
   },
   "author": "Inngest Inc. <[email protected]>",
   "license": "Apache-2.0",
-  "devDependencies": {
-    "@jest/globals": "^29.5.0"
-  },
   "dependencies": {
+    "tinyspy": "^3.0.2",
     "ulid": "^2.3.0"
+  },
+  "peerDependencies": {
+    "inngest": "^3.22.12"
+  },
+  "devDependencies": {
+    "prettier": "^3.1.0"
   }
 }