Add test for variants if using special selectors

Signed-off-by: Marcel Bargull <marcel.bargull@udo.edu>

tests/test-recipes/variants/32_variant_implicit_via_special_selector/meta.yaml

@@ -0,0 +1,13 @@
+package:
+  name: test_variant_implicit_via_special_selector
+  version: 1.0
+
+build:
+  # "python" variant implicitly injected via "py" selector, but not explicit.
+  skip: true  # [py<33]
+
+outputs:                                                         # [with_outputs]
+  - name: test_variant_implicit_via_special_selector_subpackage  # [with_outputs]
+    requirements:                                                # [with_outputs]
+      host:                                                      # [with_outputs]
+        - python                                                 # [with_outputs]

tests/test_variants.py

@@ -14,6 +14,7 @@
 from conda_build import api, exceptions
 from conda_build.utils import ensure_list, package_has_file
 from conda_build.variants import (
+    PACKAGE_SELECTOR_MAP,
     combine_specs,
     dict_of_lists_to_list_of_dicts,
     filter_combined_spec_to_used_keys,
@@ -660,6 +661,19 @@ def test_variant_subkeys_retained():
     get_all_replacements(outputs[0][1].config.variant)
 
 
+@pytest.mark.parametrize("with_outputs", [False, True])
+def test_variant_implicit_via_special_selector(with_outputs):
+    ms = api.render(
+        os.path.join(variants_dir, "32_variant_implicit_via_special_selector"),
+        variants={"python": ["2.7", "3.3", "3.4"], "with_outputs": [with_outputs]},
+        finalize=False,
+        bypass_env_check=True,
+    )
+    assert sorted(m.config.variant["python"] for m, _, _ in ms) == ["3.3", "3.4"]
+    for m, _, _ in ms:
+        assert m.get_used_vars().intersection(PACKAGE_SELECTOR_MAP) == {"python"}
+
+
 @pytest.mark.parametrize(
     "internal_defaults, low_prio_config, high_prio_config, expected",
     [