[diffusion] fix: fix Flux.2 condition image resize (#14232)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

python/sglang/multimodal_gen/test/server/testcase_configs.py

@@ -125,7 +125,7 @@ class DiffusionServerArgs:
 class DiffusionSamplingParams:
     """Configuration for a single model/scenario test case."""
 
-    output_size: str = "1024x1024"  # output image dimensions (or video resolution)
+    output_size: str = ""
 
     # inputs and conditioning
     prompt: str | None = None  # text prompt for generation
@@ -310,6 +310,19 @@ ONE_GPU_CASES_B: list[DiffusionTestCase] = [
     #     warmup_edit=0,
     #     custom_validator="video",
     # ),
+    DiffusionTestCase(
+        "flux_2_ti2i",
+        DiffusionServerArgs(
+            model_path="black-forest-labs/FLUX.2-dev",
+            modality="image",
+            warmup_text=0,
+            warmup_edit=1,
+        ),
+        DiffusionSamplingParams(
+            prompt="Convert 2D style to 3D style",
+            image_path="https://github.com/lm-sys/lm-sys.github.io/releases/download/test/TI2I_Qwen_Image_Edit_Input.jpg",
+        ),
+    ),
     DiffusionTestCase(
         "fast_hunyuan_video",
         DiffusionServerArgs(