Add property-based tests using Hypothesis

property_tests.py checks general properties of jsonpatch against generated
documents and patches:

- make_patch: diffing equal documents gives an empty patch, applying
  make_patch(src, dst) to src gives dst, inputs are not modified, the
  result shares no objects with dst
- apply_patch: the document and the patch are not modified, only
  JsonPatchException / JsonPointerException are raised (also for
  malformed patches), in_place and string patches give the same result
- single operations: whole-document targets and sources, moving into
  own children, replace of any existing location, 'test' using JSON
  equality
- JsonPatch: string roundtrip, equal patches have equal hashes
- a state machine applying random valid operations and comparing each
  result with a direct implementation of RFC 6902

Properties that do not hold yet are expected failures, each pinned to the
minimal counterexample Hypothesis found. Among them are known issues
(#124, #137, #138, #179, #180, #190) and some that appear to be
unreported: make_patch mishandling object keys that int() accepts,
replace rejecting the object member '-', hash() failing for patches with
array/object values, 'test' treating 1 and true as equal, copy from the
whole document failing, and moves into own children being allowed for
array members.

The tests run in CI and via "make test".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JqGXptMsaz9bfrMoaMpZ1A

Author: claude

.github/workflows/test.yaml

@@ -20,7 +20,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install flake8 pytest
+          pip install flake8 pytest hypothesis
           if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
           pip install coveralls
 #      - name: Lint with flake8
@@ -32,3 +32,6 @@ jobs:
       - name: Test
         run: |
           coverage run --source=jsonpointer tests.py
+      - name: Property-based tests
+        run: |
+          python property_tests.py

.gitignore

@@ -4,3 +4,4 @@ build
 dist
 *.egg-info/
 doc/_build
+.hypothesis

README.md

@@ -26,3 +26,14 @@ Running external tests
 To run external tests (such as those from https://github.com/json-patch/json-patch-tests) use ext_test.py
 
     ./ext_tests.py ../json-patch-tests/tests.json
+
+Running property-based tests
+----------------------------
+Property-based tests using [Hypothesis](https://hypothesis.readthedocs.io/)
+are in property_tests.py. Properties that the implementation does not satisfy
+yet are marked as expected failures.
+
+    pip install hypothesis
+    python property_tests.py
+
+Set `HYPOTHESIS_PROFILE=thorough` to run many more examples.

makefile

@@ -11,6 +11,7 @@ help:
 
 test:
 	python -Wd -m coverage run --branch --source=jsonpatch tests.py
+	python -Wd property_tests.py
 	coverage report --show-missing
 
 coverage: