fix: raise instead of printing None when hello_world output lacks text

find_main_content() can return a content dict that has no `text` key
(schema mismatch or unexpected API output). Previously hello_world()
did `print(content.get("text"))`, which printed `None` and exited
successfully — a silent failure that the API-hitting e2e test could not
catch. Guard the value: raise RuntimeError unless `text` is a non-empty
string, mirroring the existing `content is None` check.

Add tests/unit/test_hello_world.py — an offline regression test (no
pipelex_api/inference marker, runs in CI) that patches the API client
with a hand-rolled async fake and asserts the missing-text path raises.

Resolves greptile review comment on PR #57.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ry9KASVKXj1SVgJqtrSMxh

Author: lchoquel

my_project/hello_world.py

@@ -63,8 +63,12 @@ async def hello_world() -> None:
     if content is None:
         raise RuntimeError("The pipeline returned no output content.")
 
+    generated_text = content.get("text")
+    if not isinstance(generated_text, str) or not generated_text:
+        raise RuntimeError("The pipeline returned no text output.")
+
     print("Your first Pipelex output:\n")
-    print(content.get("text"))
+    print(generated_text)
 
 
 if __name__ == "__main__":

tests/unit/test_hello_world.py

@@ -0,0 +1,53 @@
+from typing import Any
+
+import pytest
+from pytest import CaptureFixture, MonkeyPatch
+
+from my_project import hello_world as hello_world_module
+from my_project.hello_world import hello_world
+
+
+class _FakeResults:
+    # Minimal stand-in for pipelex_sdk.runs.RunResults: find_main_content()
+    # reads only `.main_stuff` / `.pipe_output`.
+    def __init__(self, main_stuff: Any) -> None:
+        self.main_stuff = main_stuff
+        self.pipe_output = None
+
+
+class _FakeClient:
+    # Stand-in for PipelexAPIClient used as `async with ... as client`, so no
+    # network is touched: __aenter__ returns the client and start_and_wait
+    # yields the canned results.
+    def __init__(self, results: _FakeResults) -> None:
+        self._results = results
+
+    async def __aenter__(self) -> "_FakeClient":
+        return self
+
+    async def __aexit__(self, *_exc_info: object) -> None:
+        return None
+
+    async def start_and_wait(self, *, pipe_code: str, mthds_contents: list[str]) -> _FakeResults:
+        return self._results
+
+
+class TestHelloWorldOutput:
+    def _patch_client(self, monkeypatch: MonkeyPatch, main_stuff: Any) -> None:
+        results = _FakeResults(main_stuff=main_stuff)
+        monkeypatch.setattr(hello_world_module, "PipelexAPIClient", lambda: _FakeClient(results))
+
+    async def test_missing_text_raises(self, monkeypatch: MonkeyPatch):
+        # A valid content dict without a `text` key must fail loudly instead of
+        # printing `None` and exiting successfully.
+        self._patch_client(monkeypatch, main_stuff={"not_text": "oops"})
+
+        with pytest.raises(RuntimeError, match="no text output"):
+            await hello_world()
+
+    async def test_valid_text_prints(self, monkeypatch: MonkeyPatch, capsys: CaptureFixture[str]):
+        self._patch_client(monkeypatch, main_stuff={"text": "a generated haiku"})
+
+        await hello_world()
+
+        assert "a generated haiku" in capsys.readouterr().out