test(http): add unit tests for SSE stream parser and fallback responses

Author: Iwaniukooo11

tests/client/transports/test_http_helpers.py

@@ -0,0 +1,64 @@
+import httpx
+import pytest
+
+from a2a.client.errors import A2AClientError
+from a2a.client.transports.http_helpers import (
+    _default_sse_error_handler,
+    parse_sse_stream,
+    send_http_stream_request,
+)
+
+
+def test_default_sse_error_handler():
+    with pytest.raises(
+        A2AClientError, match='SSE stream error event received: error_msg'
+    ):
+        _default_sse_error_handler('error_msg')
+
+
+@pytest.mark.asyncio
+async def test_parse_sse_stream_edge_cases():
+    async def mock_aiter_lines():
+        yield ': comment line (should be ignored)\n'
+        yield 'event: custom_event\n'
+        yield 'data:  hello\n'
+        yield 'data: world\n'
+        yield '\n'
+        yield '\n'
+        yield 'data: \n'
+        yield '\n'
+
+    response = httpx.Response(200)
+    response.aiter_lines = mock_aiter_lines  # type: ignore
+
+    events = [e async for e in parse_sse_stream(response)]
+    assert events == [
+        ('custom_event', ' hello\nworld'),
+        ('message', ''),
+    ]
+
+
+@pytest.mark.asyncio
+async def test_send_http_stream_request_non_sse(mocker):
+    client = httpx.AsyncClient()
+    request = httpx.Request('GET', 'http://test')
+    response = httpx.Response(
+        200,
+        headers={'Content-Type': 'application/json'},
+        content=b'plain error response',
+        request=request,
+    )
+
+    mocker.patch(
+        'a2a.client.transports.http_helpers._SSEEventSource.__aenter__',
+        return_value=response,
+    )
+    mocker.patch(
+        'a2a.client.transports.http_helpers._SSEEventSource.__aexit__',
+        return_value=None,
+    )
+
+    chunks = [
+        c async for c in send_http_stream_request(client, 'GET', 'http://test')
+    ]
+    assert chunks == ['plain error response']