test: cover Ollama health check outcomes

- Verify healthy responses return true
- Verify non-OK HTTP responses return false
- Verify network failures return false without propagating errors
- Restore the global fetch implementation after each test

src/ollama.test.ts

@@ -1,7 +1,7 @@
 import assert from "node:assert/strict";
 import { it } from "node:test";
 
-import { generateResponse } from "./ollama.js";
+import { checkOllamaHealth, generateResponse } from "./ollama.js";
 
 it("returns generated text from Ollama", async () => {
   const originalFetch = globalThis.fetch;
@@ -79,3 +79,38 @@ it("propagates an error when an Ollama request times out", async () => {
     globalThis.fetch = originalFetch;
   }
 });
+
+it("returns true when Ollama is healthy", async () => {
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = async () => new Response("{}", { status: 200 });
+
+  try {
+    assert.equal(await checkOllamaHealth(), true);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});
+
+it("returns false when Ollama returns a non-OK health response", async () => {
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = async () => new Response("Unavailable", { status: 503 });
+
+  try {
+    assert.equal(await checkOllamaHealth(), false);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});
+
+it("returns false when Ollama is unreachable during a health check", async () => {
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = async () => {
+    throw new TypeError("fetch failed");
+  };
+
+  try {
+    assert.equal(await checkOllamaHealth(), false);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});