Remove site-wide dependency on setuptools in test suite

test/site/BUILD

@@ -0,0 +1,13 @@
+subinclude("//build_defs:python")
+
+python_test(
+    name = "site_test",
+    srcs = ["site_test.py"],
+    site = True,
+)
+
+python_test(
+    name = "no_site_test",
+    srcs = ["no_site_test.py"],
+    site = False,
+)

test/site/no_site_test.py

@@ -0,0 +1,9 @@
+import sys
+import unittest
+
+
+class NoSiteTest(unittest.TestCase):
+
+    def test_no_site_flag_passed(self):
+        """Ensures that the Python interpreter was invoked with the -S option."""
+        self.assertTrue(sys.flags.no_site)

test/site/site_test.py

@@ -0,0 +1,9 @@
+import sys
+import unittest
+
+
+class SiteTest(unittest.TestCase):
+
+    def test_no_site_flag_not_passed(self):
+        """Ensures that the Python interpreter was *not* invoked with the -S option."""
+        self.assertFalse(sys.flags.no_site)