feat: add gemini-2.5-flash-image backend to google_imagen

tests/tools/test_google_imagen_gemini_backend.py

@@ -0,0 +1,131 @@
+"""Tests for the Gemini image backend in google_imagen.
+
+Models named `gemini-*` (e.g. gemini-2.5-flash-image) are not served by the
+Imagen `:predict` endpoint — they generate images through generate_content
+with an image_config. This backend matters on Vertex projects that have no
+Imagen catalog access, where it is the only working Google image path.
+"""
+
+import sys
+import types as pytypes
+from pathlib import Path
+
+import pytest
+
+PROJECT_ROOT = Path(__file__).resolve().parent.parent.parent
+sys.path.insert(0, str(PROJECT_ROOT))
+
+
+class _FakeInline:
+    def __init__(self, data: bytes):
+        self.data = data
+
+
+class _FakePart:
+    def __init__(self, data: bytes):
+        self.inline_data = _FakeInline(data)
+
+
+class _FakeContent:
+    def __init__(self, parts):
+        self.parts = parts
+
+
+class _FakeCandidate:
+    def __init__(self, parts):
+        self.content = _FakeContent(parts)
+
+
+class _FakeResponse:
+    def __init__(self, parts):
+        self.candidates = [_FakeCandidate(parts)]
+
+
+@pytest.fixture
+def imagen_tool(monkeypatch):
+    monkeypatch.setenv("GOOGLE_API_KEY", "test-key")
+
+    calls: list[dict] = []
+
+    class _FakeModels:
+        def generate_content(self, model=None, contents=None, config=None):
+            calls.append({"model": model, "contents": contents, "config": config})
+            return _FakeResponse([_FakePart(b"GEMINI_IMG")])
+
+    class _FakeClient:
+        models = _FakeModels()
+
+    import tools.google_credentials as gc
+
+    monkeypatch.setattr(
+        gc, "get_genai_client", lambda http_options=None, location=None: _FakeClient()
+    )
+
+    from tools.graphics.google_imagen import GoogleImagen
+
+    return GoogleImagen(), calls
+
+
+def test_gemini_model_routes_to_generate_content(imagen_tool, tmp_path):
+    tool, calls = imagen_tool
+    out = tmp_path / "img.png"
+
+    result = tool.execute(
+        {
+            "prompt": "a flower",
+            "model": "gemini-2.5-flash-image",
+            "aspect_ratio": "16:9",
+            "output_path": str(out),
+        }
+    )
+
+    assert result.success
+    assert result.data["model"] == "gemini-2.5-flash-image"
+    assert out.read_bytes() == b"GEMINI_IMG"
+
+    assert len(calls) == 1
+    assert calls[0]["model"] == "gemini-2.5-flash-image"
+    # Aspect ratio must reach the API through image_config, not be dropped.
+    assert calls[0]["config"].image_config.aspect_ratio == "16:9"
+
+
+def test_gemini_cost_estimate_is_per_image():
+    from tools.graphics.google_imagen import GoogleImagen
+
+    tool = GoogleImagen()
+    assert tool.estimate_cost(
+        {"model": "gemini-2.5-flash-image", "number_of_images": 2}
+    ) == pytest.approx(0.039 * 2)
+
+
+def test_text_only_response_is_a_clear_error(monkeypatch, tmp_path):
+    monkeypatch.setenv("GOOGLE_API_KEY", "test-key")
+
+    class _TextPart:
+        inline_data = None
+
+    class _FakeModels:
+        def generate_content(self, model=None, contents=None, config=None):
+            return _FakeResponse([_TextPart()])
+
+    class _FakeClient:
+        models = _FakeModels()
+
+    import tools.google_credentials as gc
+
+    monkeypatch.setattr(
+        gc, "get_genai_client", lambda http_options=None, location=None: _FakeClient()
+    )
+
+    from tools.graphics.google_imagen import GoogleImagen
+
+    result = GoogleImagen().execute(
+        {
+            "prompt": "a flower",
+            "model": "gemini-2.5-flash-image",
+            "output_path": str(tmp_path / "img.png"),
+        }
+    )
+
+    assert not result.success
+    assert "No image data" in result.error