test: add start of Assistant class type tests.

test/types/assistant.test-d.ts

@@ -0,0 +1,35 @@
+import { expectError, expectType } from 'tsd';
+import { Assistant } from '../../src/Assistant';
+
+// Constructor tests
+const asyncNoop = () => Promise.resolve();
+// missing required properties `threadStarted` and `userMessage`
+expectError(new Assistant({}));
+// missing required property `threadStarted`
+expectError(
+  new Assistant({
+    userMessage: asyncNoop,
+  }),
+);
+// missing required property `userMessage`
+expectError(
+  new Assistant({
+    threadStarted: asyncNoop,
+  }),
+);
+// happy construction
+expectType<Assistant>(
+  new Assistant({
+    threadStarted: asyncNoop,
+    userMessage: asyncNoop,
+  }),
+);
+
+// threadStarted tests
+new Assistant({
+  userMessage: asyncNoop,
+  threadStarted: async ({ saveThreadContext }) => {
+    expectType<void>(await saveThreadContext());
+    return Promise.resolve();
+  },
+});