Add test coverage for delegated hash bins

This change adds tests coverage for `path_hash_prefixes` and
verifies that role names matching specific prefixed successfully
find and download the corresponding metadata files and do not
succeed to find existing, but non-matching files

Signed-off-by: Ivana Atanasova <[email protected]>

Author: ivanayov

tests/test_updater_delegation_graphs.py

@@ -363,6 +363,120 @@ def test_safely_encoded_rolenames(self) -> None:
         self.assertListEqual(self.sim.fetch_tracker.metadata, exp_calls)
 
 
+    hash_bins_metadata: utils.DataSet = {
+        "delegated hash bins": DelegationsTestCase(
+            delegations=[
+                TestDelegation("targets", "f8-ff", paths=None, path_hash_prefixes=[
+                        "f8",
+                        "f9",
+                        "fa",
+                        "fb",
+                        "fc",
+                        "fd",
+                        "fe",
+                        "ff",
+                    ]),
+                TestDelegation("targets", "20-27", paths=None, path_hash_prefixes=[
+                        "20",
+                        "21",
+                        "22",
+                        "23",
+                        "24",
+                        "25",
+                        "26",
+                        "27",
+                    ]),
+            ],
+            target_files=[
+                TestTarget(
+                    "f8-ff",
+                    b"fff0838676c1dacb8827b02511e89f85b43814a74dd2c3ffb31d952a1db94311",
+                    "non_matching_path_to_prefix.ext",
+                ),
+                TestTarget(
+                    "20-27",
+                    b"22992ae806e6d652835f3c84e169f05127da69e599f902e4dbdc6ff27ce46d01",
+                    "delegate_1.ext",
+                ),
+            ],
+            visited_order=["f8-ff", "20-27"],
+        ),
+    }
+
+    @utils.run_sub_tests_with_dataset(hash_bins_metadata)
+    def test_delegated_hash_bins(self, test_data: DelegationsTestCase) -> None:
+        try:
+            self._init_repo(test_data)
+            self.setup_subtest()
+
+            updater = self._init_updater()
+            # Call explicitly refresh to simplify the expected_calls list
+            updater.refresh()
+            self.sim.fetch_tracker.metadata.clear()
+
+            roles_pref_map = [
+                (
+                    "f8-ff",
+                    [
+                        "f8",
+                        "f9",
+                        "fa",
+                        "fb",
+                        "fc",
+                        "fd",
+                        "fe",
+                        "ff",
+                    ],
+                ),
+                (
+                    "20-27",
+                    [
+                        "20",
+                        "21",
+                        "22",
+                        "23",
+                        "24",
+                        "25",
+                        "26",
+                        "27",
+                    ],
+                ),
+            ]
+
+            delegated_role1 = DelegatedRole(
+                roles_pref_map[0][0], [], 1, False, roles_pref_map[0][1]
+            )
+            delegated_role1.path_hash_prefixes = roles_pref_map[0][1]
+
+            delegated_role2 = DelegatedRole(
+                roles_pref_map[1][0], [], 1, False, roles_pref_map[1][1]
+            )
+            delegated_role2.path_hash_prefixes = roles_pref_map[1][1]
+
+            spec_version = ".".join(SPECIFICATION_VERSION)
+            targets = Targets(1, spec_version, self.sim.safe_expiry, {}, None)
+            self.sim.add_delegation("targets", delegated_role1, targets)
+            self.sim.add_delegation("f8-ff", delegated_role2, targets)
+
+            # verify that no metadata file was downloaded as expected
+            # for non-existing path
+            target_info = updater.get_targetinfo("missingpath")
+            self.assertIsNone(target_info)
+
+            # verify that no metadata file was downloaded for existing
+            # path that doesn't match correct prefix
+            target_info = updater.get_targetinfo("non_matching_path_to_prefix.ext")
+            self.assertIsNone(target_info)
+
+            # verify that the target info was successfully found 
+            # and the correct delegated metadata file was downloaded
+            target_info = updater.get_targetinfo("delegate_1.ext")
+            assert target_info is not None
+            self.assertEqual(target_info.path, "delegate_1.ext")
+
+        finally:
+            self.teardown_subtest()
+
 class TestTargetFileSearch(TestDelegations):
     r"""
     Create a single repository with the following delegations: