# Tests

Tests are part of the build. If your tests are failing, your build is failing:
test errors arrive in the same diagnostic stream as compile errors, and a
release does not happen until every test passes. Save a file and the tests
whose dependencies changed run, on a pool of concurrent workers, each inside a
Postgres transaction that rolls back when it ends. Results land in the editor,
in `elements build -json`, and in the test tree.

The test API ships with `@elements/app`: `test`, `assert`, `equal`, `errorf`,
and `fatalf`, composed through nested `test()` blocks. No runner to configure,
no setup or teardown.

## At a Glance

```ts
// app/lib/utils.test.ts
import { test, assert, equal, errorf, fatalf, sql } from "@elements/app";

test("users", () => {
  test("create", () => {
    let user = sql<User>(`insert into users (name, email) values ('alice', 'a@x.com') returning *`).firstOrThrow();
    assert(user.name === "alice");
    equal(user.email, "a@x.com");
  });

  test("validate email shape", () => {
    if (!"alice@x.com".includes("@")) {
      errorf("expected %v to contain @", "alice@x.com");
    }
  });

  test("hits the database", () => {
    let row = sql<{ n: number }>(`select 1 as n`).firstOrThrow();
    equal(row.n, 1);
  });
});
```

That is a complete test file. No setup, no teardown, no `beforeEach`. The
transaction wrapper handles cleanup. Save the file and tests run.

## The API

Sync-style. The compiler propagates async automatically.

- `test(desc, fn)`: defines a test block. Nested `test()` calls produce child
  blocks. Tests run sequentially within a parent.
- `assert(cond, msg?)`: records an error if `cond` is false. Continues.
- `equal(actual, expected, msg?)`: deep equality. Records an error showing both
  values if not equal. Continues.
- `errorf(fmt, ...args)`: records a formatted error. Uses `%v` placeholders.
  Continues.
- `fatalf(fmt, ...args)`: records a formatted error and stops the current test
  block immediately. Same `%v` placeholders as `errorf`.

There is no async variant. `test` takes an `async` callback, so there is nothing
to switch to; see the sync-style section below. The assertions themselves are
synchronous because they record errors and return.

## Auto-Rollback Transactions

Every `test()` is isolated and rolls back when it ends. A top-level test runs in
its own transaction; a nested test runs in a savepoint on its parent's
connection. Either way the rows a test writes are gone when it finishes, and a
sibling never sees them. No cleanup code needed.

```ts
test("users", () => {
  test("insert a row", () => {
    sql(`insert into users (name) values ('alice')`);
    let count = sql<{ n: number }>(`select count(*) as n from users`).firstOrThrow();
    equal(count.n, 1);
  });

  test("does not see the previous test's row", () => {
    let count = sql<{ n: number }>(`select count(*) as n from users`).firstOrThrow();
    equal(count.n, 0);
  });
});
```

`sql()` calls inside the test automatically use the transaction. Nothing to
pass.

A SQL error in one test rolls back to that test's savepoint, so the next test
still runs against a clean connection.

## Opting Out of the Transaction

Some tests need real commits: verifying a commit-time trigger, or code that
spans several transactions. Add the `@test tx=false` build tag to the file. Its
tests then commit for real, and cleanup is yours to handle.

```ts
/** @test tx=false */

test("real commit path", () => {
  tx(() => {
    sql(`insert into events (name) values ('committed')`);
  });

  let row = sql<Event>(`select * from events where name = 'committed'`).firstOrThrow();
  equal(row.name, "committed");

  sql(`delete from events where name = 'committed'`);
});
```

Opting out is per file, not per test: a real commit cannot live inside an outer
rollback, so the setting applies to the whole file.

## File Layout

Test files are named `test.ts` or `<name>.test.ts`. They live anywhere in the
tree.

```
app/
  pages/home/
    index.ts
    template.ehtml
    test.ts                  # tests for the home page
  lib/
    utils.ts
    utils.test.ts            # tests for utils
    parser.test.ts           # tests for parser
```

Scaffold a test for an existing file:

```
elements create test app/lib/utils.ts
```

## Session in Tests

`session` is available inside tests. The session is a fresh empty session per
test body. Log in to it explicitly when a test needs an authenticated context.

```ts
import { test, session, sql } from "@elements/app";

test("my profile returns the logged-in user", () => {
  let user = sql<User>(`insert into users (name) values ('alice') returning *`).firstOrThrow();
  session.login({ userId: user.id, userName: user.name });

  let me = getMyProfile();
  equal(me.id, user.id);
});
```

The next test starts with no logged-in user. No teardown needed.

## Running Tests

Watch mode is the default in a tty:

```
elements test                          # all tests, watch mode
elements test app/pages/home/test.ts   # specific file
elements test app/lib/*.test.ts        # shell glob expands to matching files
```

You get an interactive tree view. The same view is used by `elements start` when
tests fail.

For machine-readable output:

```
elements test -json
elements test path/test.ts -json
```

`-json` returns the test tree as structured data. Build and test state lives in
the project server, so `elements test -json` is instant and atomic across
multiple callers.

## Tests as Part of the Build

In Elements, "build" means: get the app ready for release. Tests are part of
that. Every save runs the tests whose source dependencies changed, and only
those: a test that did not depend on the changed code does not re-run, and a
test whose dependencies have an error does not run at all until the error is
fixed. Failing tests block the release, so `.elements/release` only ever holds
an app whose tests passed.

Why this is fast enough to run on every save:

- A pool of test workers, one per CPU by default, runs test files in parallel.
- Only tests whose dependency graph changed re-run. The rest report their
  cached result.
- The workers are hot reloaded like the app: a save swaps the changed modules
  into running worker processes rather than starting new ones.
- Each test is isolated by a transaction at the top level and a savepoint when
  nested, so there is no per-test setup beyond opening it.

## There Is No CI Layer

The loop that runs tests on your save is the same loop that runs them on a
deploy. `elements deploy` builds on the target machine against its own test
database, and the release does not go live until every test passes there; a
failure aborts the deploy and the previous release stays up (see
`deploy/environments`). Tests therefore run in three places with one
definition: your editor as you type, your machine when you build, and the
machine you ship to before it switches over. There is no pipeline to write, no
runner to keep in sync with local, and no waiting for a queue to tell you what
your editor already told you.

## Two Databases

Every environment, development included, has an app database and a test
database, `<app>` and `<app>_test`. Migrations run against the test database
before tests, and against the app database before release. Tests never touch
the data you are looking at in the browser, and a migration that breaks a test
never reaches the app database.

## Sync-Style Code

Tests are sync-style. The compiler converts to async at build time. You don't
need to write `async` or `await` unless you want to. The test body reads as a
sequence of statements.

```ts
test("create", () => {
  let user = sql(`insert into users (name) values ('a') returning *`).firstOrThrow();
  assert(user.name === "a");
});
```

`test` accepts an `async` callback, so a body may be sync, async, or a mix of
both. All three of these are correct:

```ts
test("sync", () => { post("a"); });
test("async", async () => { await post("b"); });
test("mixed", async () => { await post("c"); count(); });
```

**Do not write `await` on a sync-style call.** The compiler inserts it. If you
write it yourself you get "'await' expressions are only allowed within async
functions". Marking the callback `async` is a detour; delete the `await`
instead.

**There is no `testAsync`.** It used to exist and it was a trap: it was `test`
minus the compiler's `await`, which bought nothing and cost isolation. A nested
block with no `await` registers its reporting node but leaves nobody owning its
promise, and the savepoint isolation described above depends on nested tests
running serially.

`Promise.all` needs no special variant either. It works in a `test` body like
anywhere else. It will not make queries concurrent inside a test: a
test runs on one connection and Postgres serialises on it. Two 300 ms queries
through `Promise.all` take 600 ms, the same as writing them one after the other.

## Viewing the Test Tree

`elements test` (in a tty) opens a live tree view. Tests are organized by file
and nested `test()` blocks. Each leaf shows pass, fail, or skip with the failure
message inline.

Keyboard:

- `j` / `k`: navigate.
- `Enter`: expand or collapse.
- `y`: copy the current selection.
- `ctrl-c`: exit.

The tree updates live as new test results arrive.

## Nesting

```ts
test("login", () => {
  test("with valid credentials", () => { /* ... */ });
  test("with invalid credentials", () => { /* ... */ });
  test("with locked account", () => { /* ... */ });
});
```

Nesting is for organization. Tests run sequentially within a parent. Each child
runs in its own savepoint on the parent's connection and rolls back when it
ends, so siblings stay isolated. Rows a parent writes before its children run
are visible to every child.

## What Counts as a Test Failure

- `assert(false)`: records `Assert`, continues.
- `equal(actual, expected)` mismatch: records `Equal` with both values,
  continues.
- `errorf(...)`: records `Errorf`, continues.
- `fatalf(...)`: records `Fatal` and stops the block.
- Any thrown `Error` outside of `fatalf`: records `Crash`, stops the block.
- A test that exceeds its timeout: records `Timeout`, stops the block.

`fatalf` is the explicit "stop now" signal. Everything else accumulates errors
and lets the test continue, which is useful for assertions in a loop.

`assert` is also usable in application code, and there it depends on whether a
test is on the stack. In a request it throws, as you would expect. Called from
code a test is exercising, it records a failure against that test and lets
execution continue, so the same line behaves differently under test than it
does in production. That is deliberate, and it means an `assert` buried in app
code can fail a test at a line that is not in the test file.

## Testing That Code Throws

A bare thrown error records a `Crash` and stops the block, so to assert that a
call *should* throw, catch it yourself. Verify both that it threw and that the
error was the expected kind.

```ts
import { test, session, assert, AuthError } from "@elements/app";

test("posting while logged out is rejected", () => {
  let threw = false;

  try {
    createPost({ title: "hi" });
  } catch (err) {
    threw = true;
    assert(err instanceof AuthError, `got ${err}`);
  }

  assert(threw);
});
```

**Put the error in the message.** Without `` `got ${err}` ``, when the call
throws something unexpected (usually a real bug, not the rejection you were
testing for), the assertion fails with `assertion failed` and the actual error,
its type and its message are discarded. Interpolating `err` costs nothing when
the test passes and is the whole diagnosis when it does not.

A failed `assert` records and continues, and anchors to the line it is written
on. Factor this shape into a helper and every throw-test in the file reports at
that one line inside the helper, not at the test that called it. Interpolating
the error is what keeps such a helper readable.

A helper that takes the call as a callback has to be `async` and `await` it.
Once it is `async`, the compiler stops awaiting calls to it, so write
`await expectError(...)` in an `async` test. An unawaited helper runs after the
test has ended, against a rolled-back savepoint and whatever session the test
logged in last, and reports failures that did not happen.

The `threw` flag makes the test fail when the call unexpectedly *succeeds*;
without it, a call that never throws passes. Use the same shape for `ValidationError` on bad input,
`ForbiddenError` on a role check, and so on.

## Testing a LiveTable Write

`insert`, `update`, and `delete` work on the server, so a test calls them the
same way a template does: on a view. `table.view()` opens one, exactly as a
route would, and the write runs the real path: partition check, your handler
or auto-SQL, then the broadcast.

```ts
import { test, equal, session, sql } from "@elements/app";
import { comments } from "./services";

test("a member can comment", () => {
  session.login({ userId: "u1", userName: "alice" });

  comments.view().insert({ text: "hi", author: "alice" });

  equal(sql(`select text from comments`).firstOrThrow().text, "hi");
});
```

A partition is passed here too: `comments.view({ roomId })`.

The session is the one the test is running in, so a handler's session check
sees exactly what a request would. A test that logs nobody in is an anonymous
caller, which is how you test that a write is refused:

```ts
test("an anonymous visitor cannot comment", () => {
  let threw = false;

  try {
    comments.view().insert({ text: "nope", author: "nobody" });
  } catch (err) {
    threw = true;
    assert(err instanceof AuthError, `got ${err}`);
  }

  assert(threw);
  equal(sql(`select count(*) from comments`).firstOrThrow().count, 0);
});
```

Write the mutation somewhere a test can import. A helper defined inside a
`template.ehtml` is reachable only from that template, so a write worth testing
belongs in the page's `services.ts` or in `app/shared/services/`. Give it the
view as a parameter. The template passes the one the route opened, and the test
passes one of its own:

```ts
// services.ts
export function postComment(view: LiveView<Comment>, text: string) {
  view.insert({ text, author: session.getOrThrow("userName") });
}

// test.ts
postComment(comments.view(), "hi");
```

## Test-First Development

Write failing tests first. Define the behavior in a test, watch it fail, then
implement until it passes. The build loop makes this fast.

```
1. write test.ts that calls the not-yet-existent function and asserts the expected result.
2. save. elements build -json shows the test failing.
3. implement the function.
4. save. elements build -json shows the test passing.
```

Why this works in Elements specifically:

- The build loop is the feedback signal. Saving a file is the trigger.
- `elements build -json` returns structured pass/fail per test. An agent can
  poll it deterministically.
- Auto-rollback transactions mean tests do not leave residue between iterations.
- Tests run only the affected subgraph.

Change the code, not the test. When a test fails, the fix goes in the code under
test. You make the red report go green by implementing the behavior, never by
weakening, deleting, or rewriting the test to match what the code happens to do.
The test is the specification; edit it only when the specification itself
changes.

## Debugging

- The build state shows the failure with file path and line number.
- `elements test path/test.ts` runs only that file in the live viewer.
- `console.log` from inside a test body shows in the test output and in
  `.elements/logs/project.log`.
- The auto-rollback means you cannot inspect db state with `elements db` after a
  failure. To inspect, add `@test tx=false` to the file and read the rows back.

## Related

- `elements man database`: the test database and the auto-rollback transaction.
- `elements man build`: tests as part of the build pipeline.