python3.pkgs.pyproject-hooks: move tests to passthru

While pyproject-hooks is built using bootstrap packages, none of its
test dependencies should be, so we must move out of the derivation.

pkgs/development/python-modules/pyproject-hooks/default.nix

@@ -2,6 +2,7 @@
 , buildPythonPackage
 , fetchPypi
 , flit-core
+, pyproject-hooks
 , pytestCheckHook
 , pythonOlder
 , setuptools
@@ -30,17 +31,33 @@ buildPythonPackage rec {
     tomli
   ];
 
-  nativeCheckInputs = [
-    pytestCheckHook
-    setuptools
-    testpath
-  ];
+  # We need to disable tests because this package is part of the bootstrap chain
+  # and its test dependencies cannot be built yet when this is being built.
+  doCheck = false;
 
-  disabledTests = [
-    # fail to import setuptools
-    "test_setup_py"
-    "test_issue_104"
-  ];
+  passthru.tests = {
+    pytest = buildPythonPackage {
+      pname = "${pname}-pytest";
+      inherit version;
+      format = "other";
+
+      dontBuild = true;
+      dontInstall = true;
+
+      nativeCheckInputs = [
+        pyproject-hooks
+        pytestCheckHook
+        setuptools
+        testpath
+      ];
+
+      disabledTests = [
+        # fail to import setuptools
+        "test_setup_py"
+        "test_issue_104"
+      ];
+    };
+  };
 
   pythonImportsCheck = [
     "pyproject_hooks"