add tests for load_graph, document behaviour

conda_forge_tick/auto_tick.py

@@ -101,7 +101,6 @@
     frozen_to_json_friendly,
     get_keys_default,
     load_existing_graph,
-    load_graph,
     parse_meta_yaml,
     parse_munged_run_export,
     pluck,

conda_forge_tick/pypi_name_mapping.py

@@ -20,7 +20,7 @@
 from packaging.utils import canonicalize_name as canonicalize_pypi_name
 
 from .lazy_json_backends import LazyJson, dump, get_all_keys_for_hashmap, loads
-from .utils import as_iterable, load_existing_graph, load_graph
+from .utils import as_iterable, load_existing_graph
 
 
 class Mapping(TypedDict):

conda_forge_tick/utils.py

@@ -451,23 +451,27 @@ def dump_graph(
 def load_existing_graph(filename: str = DEFAULT_GRAPH_FILENAME) -> nx.DiGraph:
     """
     Load the graph from a file using the lazy json backend.
-    If a non-existing or empty file is encountered, a FileNotFoundError is raised.
-    If you expect the graph to possibly not exist, use load_graph.
+    If the file does not exist, it is initialized with empty JSON before performing any reads.
+    If empty JSON is encountered, a ValueError is raised.
+    If you expect the graph to be possibly empty JSON (i.e. not initialized), use load_graph.
 
     :return: the graph
+    :raises ValueError if the file contains empty JSON (or did not exist before)
     """
     gx = load_graph(filename)
     if gx is None:
-        raise FileNotFoundError(f"Graph file {filename} does not exist or is empty")
+        raise ValueError(f"Graph file {filename} contains empty JSON")
     return gx
 
 
 def load_graph(filename: str = DEFAULT_GRAPH_FILENAME) -> Optional[nx.DiGraph]:
     """
     Load the graph from a file using the lazy json backend.
-    If you expect the graph to exist, use load_existing_graph.
+    If the file does not exist, it is initialized with empty JSON.
+    If you expect the graph to be non-empty JSON, use load_existing_graph.
 
-    :return: the graph, or None if the file does not exist or is empty JSON
+    :return: the graph, or None if the file is empty JSON (or
+    :raises FileNotFoundError if the file does not exist
     """
     dta = copy.deepcopy(LazyJson(filename).data)
     if dta:

tests/test_utils.py

@@ -1,4 +1,52 @@
-from conda_forge_tick.utils import get_keys_default
+from unittest import mock
+from unittest.mock import MagicMock, mock_open
+
+import pytest
+
+from conda_forge_tick.utils import (
+    DEFAULT_GRAPH_FILENAME,
+    get_keys_default,
+    load_existing_graph,
+    load_graph,
+)
+
+EMPTY_JSON = "{}"
+DEMO_GRAPH = """
+{
+    "directed": true,
+    "graph": {
+        "outputs_lut": {
+            "package1": {
+                "__set__": true,
+                "elements": [
+                    "package1"
+                ]
+            },
+            "package2": {
+                "__set__": true,
+                "elements": [
+                    "package2"
+                ]
+            }
+        }
+    },
+    "links": [
+        {
+            "source": "package1",
+            "target": "package2"
+        }
+    ],
+    "multigraph": false,
+    "nodes": [
+        {
+            "id": "package1",
+            "payload": {
+                "__lazy_json__": "node_attrs/package1.json"
+            }
+        }
+    ]
+}
+"""
 
 
 def test_get_keys_default():
@@ -25,9 +73,76 @@ def test_get_keys_default_none():
             "bot": None,
         },
     }
-    get_keys_default(
-        attrs,
-        ["conda-forge.yml", "bot", "check_solvable"],
-        {},
-        False,
-    ) is False
+    assert (
+        get_keys_default(
+            attrs,
+            ["conda-forge.yml", "bot", "check_solvable"],
+            {},
+            False,
+        )
+        is False
+    )
+
+
+def test_load_graph():
+    with mock.patch("builtins.open", mock_open(read_data=DEMO_GRAPH)) as mock_file:
+        gx = load_graph()
+
+        assert gx is not None
+
+        assert gx.nodes.keys() == {"package1", "package2"}
+
+    mock_file: MagicMock
+    mock_file.assert_has_calls([mock.call(DEFAULT_GRAPH_FILENAME)])
+
+
+def test_load_graph_empty_graph():
+    with mock.patch("builtins.open", mock_open(read_data=EMPTY_JSON)) as mock_file:
+        gx = load_graph()
+
+        assert gx is None
+
+    mock_file: MagicMock
+    mock_file.assert_has_calls([mock.call(DEFAULT_GRAPH_FILENAME)])
+
+
+@mock.patch("os.path.exists")
+def test_load_graph_file_does_not_exist(exists_mock: MagicMock):
+    exists_mock.return_value = False
+
+    with mock.patch("builtins.open", mock_open(read_data=EMPTY_JSON)) as mock_file:
+        load_graph()
+
+    mock_file: MagicMock
+    mock_file.assert_has_calls([mock.call(DEFAULT_GRAPH_FILENAME, "w")])
+
+
+def test_load_existing_graph():
+    with mock.patch("builtins.open", mock_open(read_data=DEMO_GRAPH)) as mock_file:
+        gx = load_existing_graph()
+
+        assert gx.nodes.keys() == {"package1", "package2"}
+
+    mock_file: MagicMock
+    mock_file.assert_has_calls([mock.call(DEFAULT_GRAPH_FILENAME)])
+
+
+def test_load_existing_graph_empty_graph():
+    with mock.patch("builtins.open", mock_open(read_data=EMPTY_JSON)) as mock_file:
+        with pytest.raises(ValueError, match="empty JSON"):
+            load_existing_graph()
+
+    mock_file: MagicMock
+    mock_file.assert_has_calls([mock.call(DEFAULT_GRAPH_FILENAME)])
+
+
+@mock.patch("os.path.exists")
+def test_load_existing_graph_file_does_not_exist(exists_mock: MagicMock):
+    exists_mock.return_value = False
+
+    with mock.patch("builtins.open", mock_open(read_data=EMPTY_JSON)) as mock_file:
+        with pytest.raises(ValueError, match="empty JSON"):
+            load_existing_graph()
+
+    mock_file: MagicMock
+    mock_file.assert_has_calls([mock.call(DEFAULT_GRAPH_FILENAME, "w")])