test(mocks): extract mock python extension helper (bazel-contrib#3803)

This mock module was extracted from bazel-contrib#3802.

It provides a helper for defining a mock module for the python bzlmod
extension, which is standalone and generally useful for testing
rules_python's bzlmod extension.

Author: rickeylev

tests/support/mocks/BUILD.bazel

@@ -10,4 +10,10 @@ bzl_library(
     srcs = ["mocks.bzl"],
 )
 
+bzl_library(
+    name = "python_ext_bzl",
+    srcs = ["python_ext.bzl"],
+    deps = [":mocks_bzl"],
+)
+
 mocks_test_suite(name = "mocks_tests")

tests/support/mocks/python_ext.bzl

@@ -0,0 +1,102 @@
+"""Helper for defining a mock module for the python bzlmod extension."""
+
+load(":mocks.bzl", "mocks")
+
+def _module(name = "rules_python", is_root = True, **tags):
+    """Creates a mock Bzlmod module struct with defaulted tag lists.
+
+    Args:
+        name: The module name.
+        is_root: Whether this is the root module.
+        **tags: Lists of tag objects.
+
+    Returns:
+        A mock module struct.
+    """
+    defaulted_tags = {
+        "defaults": [],
+        "override": [],
+        "single_version_override": [],
+        "single_version_platform_override": [],
+        "toolchain": [],
+    }
+    defaulted_tags.update(tags)
+    return mocks.module(name = name, is_root = is_root, **defaulted_tags)
+
+def _override(**kwargs):
+    """Creates a mock python.override tag with default values."""
+    attrs = {
+        "add_runtime_manifest_urls": [],
+        "add_target_settings": [],
+        "available_python_versions": [],
+        "base_url": "https://github.com/astral-sh/python-build-standalone/releases/download",
+        "ignore_root_user_error": True,
+        "minor_mapping": {},
+        "register_all_versions": False,
+        "runtime_manifest_sha": "",
+    }
+    attrs.update(kwargs)
+    return mocks.tag(**attrs)
+
+def _defaults(**kwargs):
+    """Creates a mock python.defaults tag with default values."""
+    attrs = {
+        "python_version": "",
+        "python_version_env": "",
+    }
+    attrs.update(kwargs)
+    return mocks.tag(**attrs)
+
+def _single_version_override(**kwargs):
+    """Creates a mock python.single_version_override tag with default values."""
+    attrs = {
+        "distutils": None,
+        "distutils_content": "",
+        "patch_strip": 0,
+        "patches": [],
+        "python_version": "",
+        "sha256": {},
+        "strip_prefix": "python",
+        "urls": [],
+    }
+    attrs.update(kwargs)
+    return mocks.tag(**attrs)
+
+def _single_version_platform_override(**kwargs):
+    """Creates a mock python.single_version_platform_override tag with default values."""
+    attrs = {
+        "arch": "",
+        "coverage_tool": None,
+        "os_name": "",
+        "patch_strip": 0,
+        "patches": [],
+        "platform": "",
+        "python_version": "",
+        "sha256": "",
+        "strip_prefix": "python",
+        "target_compatible_with": [],
+        "target_settings": [],
+        "urls": [],
+    }
+    attrs.update(kwargs)
+    return mocks.tag(**attrs)
+
+def _toolchain(**kwargs):
+    """Creates a mock python.toolchain tag with default values."""
+    attrs = {
+        "configure_coverage_tool": False,
+        "ignore_root_user_error": True,
+        "is_default": False,
+        "python_version": "",
+    }
+    attrs.update(kwargs)
+    return mocks.tag(**attrs)
+
+python_ext = struct(
+    defaults = _defaults,
+    module = _module,
+    override = _override,
+    single_version_override = _single_version_override,
+    single_version_platform_override = _single_version_platform_override,
+    toolchain = _toolchain,
+)