test: add torch backend compilation integration tests

Real uv pip compile tests that verify each GPU backend produces the
correct torch variant: NVIDIA gets +cu126, AMD gets +rocm6.1, CPU gets
+cpu, and macOS gets default PyPI torch without GPU suffixes.

Gated behind TEST_TORCH_BACKEND=true. Added to CI:
- test-mac.yml: runs mac compile test
- test-windows.yml: runs nvidia and cpu compile tests

Author: bigcat88

.github/workflows/test-mac.yml

@@ -29,6 +29,16 @@ jobs:
           python -m venv venv
           source venv/bin/activate
           python -m pip install --upgrade pip
+          pip install pytest
           pip install -e .
+
+      - name: Test torch backend compilation (mac)
+        run: |
+          source venv/bin/activate
+          TEST_TORCH_BACKEND=true pytest tests/uv/test_torch_backend_compile.py::test_compile_mac -xvs
+
+      - name: Install and launch ComfyUI
+        run: |
+          source venv/bin/activate
           comfy --skip-prompt --workspace ./ComfyUI install --fast-deps --m-series --skip-manager
           comfy --here launch -- --cpu --quick-test-for-ci

.github/workflows/test-windows.yml

@@ -32,5 +32,21 @@ jobs:
           python -m pip install --upgrade pip
           pip install pytest
           pip install -e .
+
+      - name: Test torch backend compilation (nvidia)
+        run: |
+          .\venv\Scripts\Activate.ps1
+          $env:TEST_TORCH_BACKEND = "true"
+          pytest tests/uv/test_torch_backend_compile.py::test_compile_nvidia -xvs
+
+      - name: Test torch backend compilation (cpu)
+        run: |
+          .\venv\Scripts\Activate.ps1
+          $env:TEST_TORCH_BACKEND = "true"
+          pytest tests/uv/test_torch_backend_compile.py::test_compile_cpu -xvs
+
+      - name: Install and launch ComfyUI
+        run: |
+          .\venv\Scripts\Activate.ps1
           comfy --skip-prompt --workspace ./ComfyUI install --fast-deps --nvidia --cuda-version 12.6 --skip-manager
           comfy --here launch -- --cpu --quick-test-for-ci

tests/uv/test_torch_backend_compile.py

@@ -0,0 +1,77 @@
+"""Integration tests for torch backend compilation.
+
+These tests do real uv pip compile with a torch requirement and verify
+the compiled output contains the correct torch variant for each backend.
+
+Requires network access. Gated behind TEST_TORCH_BACKEND=true.
+"""
+
+import os
+import shutil
+from pathlib import Path
+
+import pytest
+
+from comfy_cli.constants import GPU_OPTION
+from comfy_cli.uv import DependencyCompiler
+
+pytestmark = pytest.mark.skipif(
+    os.environ.get("TEST_TORCH_BACKEND") != "true",
+    reason="Set TEST_TORCH_BACKEND=true to run torch backend integration tests",
+)
+
+_here = Path(__file__).parent.resolve()
+_temp = _here.parent / "temp" / "test_torch_backend"
+
+
+@pytest.fixture(autouse=True)
+def _setup_temp():
+    shutil.rmtree(_temp, ignore_errors=True)
+    _temp.mkdir(exist_ok=True, parents=True)
+    (_temp / "reqs.txt").write_text("torch\n")
+
+
+def _compile_for(gpu):
+    dc = DependencyCompiler(
+        cwd=_temp,
+        gpu=gpu,
+        outDir=_temp,
+        reqFilesCore=[_temp / "reqs.txt"],
+        reqFilesExt=[],
+    )
+    dc.make_override()
+    dc.compile_core_plus_ext()
+    return dc.out.read_text()
+
+
+def test_compile_nvidia():
+    content = _compile_for(GPU_OPTION.NVIDIA)
+    assert "+cu126" in content
+    assert "download.pytorch.org/whl/cu126" in content
+    assert "--extra-index-url" not in content
+
+
+def test_compile_amd():
+    content = _compile_for(GPU_OPTION.AMD)
+    assert "+rocm" in content
+    assert "download.pytorch.org/whl/rocm" in content
+    assert "--extra-index-url" not in content
+
+
+def test_compile_cpu():
+    content = _compile_for(GPU_OPTION.CPU)
+    assert "+cpu" in content
+    assert "download.pytorch.org/whl/cpu" in content
+    assert "--extra-index-url" not in content
+    # must not pull in nvidia CUDA libraries
+    assert "nvidia-" not in content
+
+
+def test_compile_mac():
+    content = _compile_for(GPU_OPTION.MAC_M_SERIES)
+    assert "torch==" in content
+    # default PyPI torch — no GPU-specific local version suffix
+    assert "+cu" not in content
+    assert "+rocm" not in content
+    assert "+cpu" not in content
+    assert "--extra-index-url" not in content