test(types): add types test

packages/casting/jsconfig.json

@@ -13,7 +13,7 @@
   "include": [
     "*.js",
     "public/**/*.js",
-    "src/**/*.js",
-    "test/**/*.js",
+    "src",
+    "test",
   ],
 }

packages/casting/src/types.js

@@ -1,6 +1,4 @@
 // Make this a module.
-import '@agoric/notifier';
-
 export {};
 
 /** @template T @typedef {import('@endo/far').ERef<T>} ERef */

packages/casting/test/types.test-d.ts

@@ -0,0 +1,30 @@
+import { E } from '@endo/far';
+import { expectType } from 'tsd';
+import type { ValueFollower } from '../src/follower-cosmjs.js';
+import { makeFollower } from '../src/follower.js';
+import { iterateLatest } from '../src/iterable.js';
+import { makeLeader } from '../src/leader-netconfig.js';
+import type { ValueFollowerElement } from '../src/types.js';
+
+type ThePublishedDatum = { a: 1; b: 'two' };
+type TheFollowerElement = ValueFollowerElement<ThePublishedDatum>;
+
+const leader = makeLeader();
+
+{
+  const f = makeFollower<ThePublishedDatum>('', leader, {});
+  expectType<ValueFollower<ThePublishedDatum>>(await f);
+
+  expectType<AsyncIterable<TheFollowerElement>>(await E(f).getLatestIterable());
+
+  expectType<AsyncIterable<TheFollowerElement>>(await E(f).getLatestIterable());
+
+  expectType<AsyncIterable<TheFollowerElement>>(
+    await E(f).getReverseIterable(),
+  );
+
+  const iter = iterateLatest(f);
+  for await (const { value } of iter) {
+    expectType<ThePublishedDatum>(value);
+  }
+}