fix: snapshot the current value of mutable objects (#12)

BREAKING CHANGE: values have to be copyable with `copy.deepcopy`

This is a behaviour which is already expected from other libraries.

syrusakbary/snapshottest#99

docs/index.md

@@ -210,10 +210,11 @@ def test_something():
 
 The code is generated in the following way:
 
-1. The code is generated with `repr(value)`
-2. Strings which contain newlines are converted to triple quoted strings.
-3. The code is formatted with black.
-4. The whole file is formatted with black if it was formatted before.
+1. The value is copied with `value = copy.deepcopy(value)`
+2. The code is generated with `repr(value)`
+3. Strings which contain newlines are converted to triple quoted strings.
+4. The code is formatted with black.
+5. The whole file is formatted with black if it was formatted before.
 
 !!! note
     The black formatting of the whole file could not work for the following reasons:

inline_snapshot/_inline_snapshot.py

@@ -1,5 +1,6 @@
 import ast
 import contextlib
+import copy
 import inspect
 import io
 import token
@@ -151,6 +152,8 @@ def __getitem__(self, item):
 
 class FixValue(GenericValue):
     def __eq__(self, other):
+        other = copy.deepcopy(other)
+
         if self._new_value is undefined:
             self._new_value = other
 
@@ -171,6 +174,8 @@ def cmp(a, b):
         raise NotImplemented
 
     def _generic_cmp(self, other):
+        other = copy.deepcopy(other)
+
         if self._new_value is undefined:
             self._new_value = other
         else:
@@ -258,6 +263,8 @@ def cmp(a, b):
 
 class CollectionValue(GenericValue):
     def __contains__(self, item):
+        item = copy.deepcopy(item)
+
         if self._new_value is undefined:
             self._new_value = [item]
         else:

tests/test_inline_snapshot.py

@@ -34,7 +34,7 @@ def test_disabled():
 def check_update(tmp_path):
     filecount = 1
 
-    def w(source, *, flags="", reported_flags=None):
+    def w(source, *, flags="", reported_flags=None, number=1):
         flags = Flags({*flags.split(",")})
         if reported_flags is None:
             reported_flags = flags
@@ -65,7 +65,7 @@ def w(source, *, flags="", reported_flags=None):
                 finally:
                     _inline_snapshot._active = False
 
-                assert len(_inline_snapshot.snapshots) == 1
+                assert len(_inline_snapshot.snapshots) == number
 
                 snapshot_flags = set()
 
@@ -77,7 +77,7 @@ def w(source, *, flags="", reported_flags=None):
 
                 changes = recorder.changes()
 
-                assert len(changes) == 1
+                assert len(changes) == number
 
                 print("changes:")
                 recorder.dump()
@@ -88,6 +88,92 @@ def w(source, *, flags="", reported_flags=None):
     return w
 
 
+def test_mutable_values(check_update):
+    assert (
+        check_update(
+            """
+l=[1,2]
+assert l==snapshot()
+l.append(3)
+assert l==snapshot()
+    """,
+            flags="create",
+            number=2,
+        )
+        == snapshot(
+            """
+l=[1,2]
+assert l==snapshot([1, 2])
+l.append(3)
+assert l==snapshot([1, 2, 3])
+"""
+        )
+    )
+
+    assert (
+        check_update(
+            """
+l=[1,2]
+assert l<=snapshot()
+l.append(3)
+assert l<=snapshot()
+    """,
+            flags="create",
+            number=2,
+        )
+        == snapshot(
+            """
+l=[1,2]
+assert l<=snapshot([1, 2])
+l.append(3)
+assert l<=snapshot([1, 2, 3])
+"""
+        )
+    )
+
+    assert (
+        check_update(
+            """
+l=[1,2]
+assert l>=snapshot()
+l.append(3)
+assert l>=snapshot()
+    """,
+            flags="create",
+            number=2,
+        )
+        == snapshot(
+            """
+l=[1,2]
+assert l>=snapshot([1, 2])
+l.append(3)
+assert l>=snapshot([1, 2, 3])
+"""
+        )
+    )
+
+    assert (
+        check_update(
+            """
+l=[1,2]
+assert l in snapshot()
+l.append(3)
+assert l in snapshot()
+    """,
+            flags="create",
+            number=2,
+        )
+        == snapshot(
+            """
+l=[1,2]
+assert l in snapshot([[1, 2]])
+l.append(3)
+assert l in snapshot([[1, 2, 3]])
+"""
+        )
+    )
+
+
 def test_comparison(check_update):
     assert check_update("assert 5==snapshot()", flags="create") == snapshot(
         "assert 5==snapshot(5)"