feat: add pytest plugin for rich explanations

beet/pytest_plugin.py

@@ -0,0 +1,91 @@
+from pprint import pformat
+
+from _pytest.assertion.util import assertrepr_compare
+
+from beet import Namespace, NamespaceContainer, Pack
+
+
+def pytest_assertrepr_compare(config, op, left, right):
+    if type(left) != type(right) or op != "==":
+        return
+
+    explanation = []
+
+    if isinstance(left, Pack):
+        if left.name != right.name:
+            explanation += ["", "Differing attribute 'name':"] + assertrepr_compare(
+                config, op, left.name, right.name
+            )[1:]
+        if left.extra != right.extra:
+            explanation += generate_explanation(config, left.extra, right.extra, "file")
+        if dict(left) != dict(right):
+            explanation += generate_explanation(config, left, right, "namespace")
+    elif isinstance(left, Namespace):
+        explanation += generate_explanation(config, left, right, "container")
+    elif isinstance(left, NamespaceContainer):
+        explanation += generate_explanation(config, left, right, "file")
+
+    if explanation:
+        return [assertrepr_compare(config, op, left, right)[0]] + explanation
+
+
+def plural(name, count):
+    return name + bool(count - 1) * "s"
+
+
+def generate_explanation(config, left, right, item_name):
+    verbose = config.getoption("verbose")
+
+    left_keys = set(left)
+    right_keys = set(right)
+
+    common = left_keys & right_keys
+    same = {key for key in common if left[key] == right[key]}
+    diff = common - same
+    extra_left = left_keys - right_keys
+    extra_right = right_keys - left_keys
+
+    yield ""
+
+    if same and verbose < 2:
+        count = len(same)
+        yield f"Omitting {count} identical {plural(item_name, count)}, use -vv to show"
+    elif same:
+        count = len(same)
+        yield f"Matching {plural(item_name, count)}:"
+        yield from pformat(list(same)).splitlines()
+
+    if diff:
+        count = len(diff)
+        yield f"Differing {plural(item_name, count)}:"
+        yield from pformat(list(diff)).splitlines()
+
+    if extra_left:
+        count = len(extra_left)
+        yield f"Left contains {count} more {plural(item_name, count)}:"
+        yield from pformat({k: left[k] for k in extra_left}).splitlines()
+
+    if extra_right:
+        count = len(extra_right)
+        yield f"Right contains {count} more {plural(item_name, count)}:"
+        yield from pformat({k: right[k] for k in extra_right}).splitlines()
+
+    if not diff:
+        return
+
+    if verbose < 1:
+        yield ""
+        yield "Use -v to get the full diff"
+        return
+
+    for k in diff:
+        yield ""
+        yield f"Drill down into differing {item_name} {k!r}:"
+
+        summary, *explanation = config.hook.pytest_assertrepr_compare(
+            config=config, op="==", left=left[k], right=right[k]
+        )[0]
+
+        yield f"  assert " + summary
+        for line in explanation:
+            yield "  " + line

pyproject.toml

@@ -45,6 +45,9 @@ mudkip = "^0.3.8"
 [tool.poetry.scripts]
 beet = "beet.toolchain.cli:main"
 
+[tool.poetry.plugins.pytest11]
+beet = "beet.pytest_plugin"
+
 [tool.black]
 target-version = ["py38"]
 include = '\.pyi?$'