feat: add torch-specific test as requested

tests/integration_rust/pypi_tests.rs

@@ -166,6 +166,7 @@ async fn test_index_strategy() {
 
 #[tokio::test]
 #[cfg_attr(not(feature = "slow_integration_tests"), ignore)]
+/// This test checks if we can pin a package from a PyPI index, by explicitly specifying the index.
 async fn test_pinning_index() {
     let pypi_indexes = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/data/pypi-indexes");
     let pypi_indexes_url = Url::from_directory_path(pypi_indexes.clone()).unwrap();
@@ -201,3 +202,43 @@ async fn test_pinning_index() {
             .join("foo-1.0.0-py2.py3-none-any.whl")
     );
 }
+
+#[tokio::test]
+#[cfg_attr(not(feature = "slow_integration_tests"), ignore)]
+/// This test checks if we can receive torch correctly from the whl/cu124 index.
+async fn pin_torch() {
+    /// Do some platform magic, as the index does not contain wheels for each platform.
+    let platform = Platform::current();
+    let platforms = match platform {
+        Platform::Linux64 => "\"linux-64\"".to_string(),
+        _ => format!("\"{platform}\", \"linux-64\"", platform = platform),
+    };
+
+    let pixi = PixiControl::from_manifest(&format!(
+        r#"
+        [project]
+        name = "pypi-pinning-index"
+        platforms = [{platforms}]
+        channels = ["conda-forge"]
+
+        [dependencies]
+        python = "~=3.12.0"
+
+        [target.linux-64.pypi-dependencies]
+        torch = {{ version = "*", index = "https://download.pytorch.org/whl/cu124" }}
+        "#,
+        platforms = platforms,
+    ));
+
+    let lock_file = pixi.unwrap().update_lock_file().await.unwrap();
+    // So the check is as follows:
+    // 1. The PyPI index is the main index-url, so normally torch would be taken from there.
+    // 2. We manually check if it is taken from the whl/cu124 index instead.
+    assert!(lock_file
+        .get_pypi_package_url("default", Platform::Linux64, "torch")
+        .unwrap()
+        .as_url()
+        .unwrap()
+        .path()
+        .contains("/whl/cu124"));
+}