diff --git a/mtg_ssm/mtg/counts.py b/mtg_ssm/mtg/counts.py
index eeb2656..e796520 100644
--- a/mtg_ssm/mtg/counts.py
+++ b/mtg_ssm/mtg/counts.py
@@ -67,8 +67,10 @@ def find_printing(cdb, set_code, name, set_number, multiverseid, strict=True):
         ])
     for snnm_key in snnm_keys:
         found_printings = cdb.set_name_num_mv_to_printings.get(snnm_key, [])
-        if len(found_printings) == 1 or found_printings and not strict:
+        if len(found_printings) == 1:
             return found_printings[0]
+        elif found_printings and not strict:
+            return sorted(found_printings, key=lambda p: p.id_)[0]
 
     return None
 
@@ -84,7 +86,7 @@ def coerce_card_row(card_count):
     return card_count
 
 
-def aggregate_print_counts(cdb, card_rows, strict=True):
+def aggregate_print_counts(cdb, card_rows, strict):
     """Given a card database Iterable[card_row], return print_counts"""
     print_counts = collections.defaultdict(
         lambda: collections.defaultdict(int))
@@ -109,7 +111,7 @@ def aggregate_print_counts(cdb, card_rows, strict=True):
             ct_name = count_type.name
             count = card_row.get(ct_name)
             if count:
-                print_counts[printing][count_type] += count
+                print_counts[printing.id_][count_type] += count
     return print_counts
 
 
@@ -117,20 +119,20 @@ def merge_print_counts(*print_counts_args):
     """Merge two sets of print_counts."""
     print_counts = new_print_counts()
     for in_print_counts in print_counts_args:
-        for printing, counts in in_print_counts.items():
+        for print_id, counts in in_print_counts.items():
             for key, value in counts.items():
-                print_counts[printing][key] += value
+                print_counts[print_id][key] += value
     return print_counts
 
 
 def diff_print_counts(left, right):
     """Subtract right print counts from left print counts."""
     print_counts = new_print_counts()
-    for printing in left.keys() | right.keys():
-        left_counts = left.get(printing, {})
-        right_counts = right.get(printing, {})
+    for print_id in left.keys() | right.keys():
+        left_counts = left.get(print_id, {})
+        right_counts = right.get(print_id, {})
         for key in left_counts.keys() | right_counts.keys():
             value = left_counts.get(key, 0) - right_counts.get(key, 0)
             if value:
-                print_counts[printing][key] = value
+                print_counts[print_id][key] = value
     return print_counts
diff --git a/mtg_ssm/mtg/models.py b/mtg_ssm/mtg/models.py
index 77f8e8f..38c89c5 100644
--- a/mtg_ssm/mtg/models.py
+++ b/mtg_ssm/mtg/models.py
@@ -2,6 +2,7 @@
 
 import datetime as dt
 import string
+import weakref
 
 VARIANT_CHARS = (string.ascii_letters + '★')
 STRICT_BASICS = {'Plains', 'Island', 'Swamp', 'Mountain', 'Forest'}
@@ -12,7 +13,7 @@ class Card:
     __slots__ = ('cdb', 'name', 'layout', 'names')
 
     def __init__(self, card_db, card_data):
-        self.cdb = card_db
+        self.cdb = weakref.proxy(card_db)
         self.name = card_data['name']
         self.layout = card_data['layout']
         self.names = card_data.get('names', [self.name])
@@ -41,7 +42,7 @@ class CardPrinting:
                  'counts')
 
     def __init__(self, card_db, set_code, card_data):
-        self.cdb = card_db
+        self.cdb = weakref.proxy(card_db)
         self.id_ = card_data['id']
         self.card_name = card_data['name']
         self.set_code = set_code
@@ -85,7 +86,7 @@ class CardSet:
                  'type_', 'online_only')
 
     def __init__(self, card_db, set_data):
-        self.cdb = card_db
+        self.cdb = weakref.proxy(card_db)
         self.code = set_data['code']
         self.name = set_data['name']
         self.block = set_data.get('block')
diff --git a/mtg_ssm/serialization/csv.py b/mtg_ssm/serialization/csv.py
index 6c98863..9609273 100644
--- a/mtg_ssm/serialization/csv.py
+++ b/mtg_ssm/serialization/csv.py
@@ -33,7 +33,7 @@ def rows_for_printings(cdb, print_counts, verbose):
     """Generator that yields csv rows from a card_db."""
     for card_set in cdb.card_sets:
         for printing in card_set.printings:
-            printing_counts = print_counts.get(printing, {})
+            printing_counts = print_counts.get(printing.id_, {})
             if verbose or any(printing_counts):
                 yield row_for_printing(printing, printing_counts)
 
@@ -58,7 +58,7 @@ def read(self, filename: str):
         """Read print counts from file."""
         with open(filename, 'r') as csv_file:
             return counts.aggregate_print_counts(
-                self.cdb, csv.DictReader(csv_file))
+                self.cdb, csv.DictReader(csv_file), strict=True)
 
 
 class CsvTerseDialect(CsvFullDialect):
diff --git a/mtg_ssm/serialization/deckbox.py b/mtg_ssm/serialization/deckbox.py
index 35a3d4a..06934c5 100644
--- a/mtg_ssm/serialization/deckbox.py
+++ b/mtg_ssm/serialization/deckbox.py
@@ -85,7 +85,7 @@ def rows_for_printing(printing, print_counts):
     }
     if name is not None:
         row_base['Name'] = name
-        row_counts = print_counts.get(printing, {})
+        row_counts = print_counts.get(printing.id_, {})
         copies = row_counts.get(counts.CountTypes.copies, 0)
         foils = row_counts.get(counts.CountTypes.foils, 0)
         if copies:
diff --git a/mtg_ssm/serialization/interface.py b/mtg_ssm/serialization/interface.py
index 2639983..feeb51d 100644
--- a/mtg_ssm/serialization/interface.py
+++ b/mtg_ssm/serialization/interface.py
@@ -6,7 +6,6 @@
 
 from mtg_ssm.mtg import card_db
 from mtg_ssm.mtg import counts
-from mtg_ssm.mtg import models
 
 
 class Error(Exception):
@@ -50,7 +49,7 @@ def write(self, filename: str, print_counts) -> None:
 
     @abc.abstractmethod
     def read(self, filename: str) -> Dict[
-            models.CardPrinting, Dict[counts.CountTypes, int]]:
+            str, Dict[counts.CountTypes, int]]:
         """Read print counts from file."""
 
     @staticmethod
diff --git a/mtg_ssm/serialization/xlsx.py b/mtg_ssm/serialization/xlsx.py
index 75893dd..cf2fcf8 100644
--- a/mtg_ssm/serialization/xlsx.py
+++ b/mtg_ssm/serialization/xlsx.py
@@ -165,7 +165,7 @@ def create_set_sheet(sheet, card_set, print_counts):
             printing.set_number,
             printing.artist,
         ]
-        row_counts = print_counts.get(printing, {})
+        row_counts = print_counts.get(printing.id_, {})
         for counttype in counts.CountTypes:
             row.append(row_counts.get(counttype))
         row.append(get_references(printing.card, exclude_sets={card_set}))
@@ -235,5 +235,5 @@ def read(self, filename: str):
                     'No known set with code {}'.format(sheet.title))
             print_counts = counts.merge_print_counts(
                 print_counts, counts.aggregate_print_counts(
-                    self.cdb, counts_from_sheet(sheet)))
+                    self.cdb, counts_from_sheet(sheet), strict=True))
         return print_counts
diff --git a/mtg_ssm/ssm.py b/mtg_ssm/ssm.py
index efb5bb3..1ddd63e 100644
--- a/mtg_ssm/ssm.py
+++ b/mtg_ssm/ssm.py
@@ -125,14 +125,22 @@ def get_serializer(cdb, dialect_mapping, filename):
     return serialization_class(cdb)
 
 
+def get_backup_name(filename):
+    """Given a filename, return a timestamped backup name for the file."""
+    basename, extension = os.path.splitext(filename)
+    extension = extension.lstrip('.')
+    now = datetime.datetime.now()
+    return '{basename}.{now:%Y%m%d_%H%M%S}.{extension}'.format(
+        basename=basename, now=now, extension=extension)
+
+
 def write_file(serializer, print_counts, filename):
     """Write print counts to a file, backing up existing target files."""
     if not os.path.exists(filename):
         print('Writing collection to file.')
         serializer.write(filename, print_counts)
     else:
-        backup_name = filename + '.bak-{:%Y%m%d_%H%M%S}'.format(
-            datetime.datetime.now())
+        backup_name = get_backup_name(filename)
         with tempfile.NamedTemporaryFile() as temp_coll:
             print('Writing to temporary file.')
             serializer.write(temp_coll.name, print_counts)
diff --git a/pytest.ini b/pytest.ini
new file mode 100644
index 0000000..d61d029
--- /dev/null
+++ b/pytest.ini
@@ -0,0 +1,2 @@
+[pytest]
+xfail_strict=true
diff --git a/tests/mtg/test_counts.py b/tests/mtg/test_counts.py
index 12eb06d..95b23c7 100644
--- a/tests/mtg/test_counts.py
+++ b/tests/mtg/test_counts.py
@@ -29,78 +29,48 @@ def test_coerce_card_row(raw_card_row, expected_card_row):
     assert counts.coerce_card_row(raw_card_row) == expected_card_row
 
 
-# aggregate_print_counts tests
-def test_apc_bad_printing(cdb):
-    card_counts = [{}]
-    with pytest.raises(counts.UnknownPrintingError):
-        counts.aggregate_print_counts(cdb, card_counts)
-
-
-def test_apc_no_counts(cdb):
-    card_counts = [{'id': TEST_PRINT_ID}]
-    print_counts = counts.aggregate_print_counts(cdb, card_counts)
-    assert not print_counts
-
-
-def test_apc_zeros(cdb):
-    card_counts = [{'id': TEST_PRINT_ID, 'copies': 0, 'foils': 0}]
-    print_counts = counts.aggregate_print_counts(cdb, card_counts)
-    assert not print_counts
-
-
-def test_apc_once(cdb):
-    print_ = cdb.id_to_printing[TEST_PRINT_ID]
-    card_counts = [{'id': TEST_PRINT_ID, 'copies': 1, 'foils': 2}]
-    print_counts = counts.aggregate_print_counts(cdb, card_counts)
-    assert print_counts == {
-        print_: {
+@pytest.mark.parametrize('card_rows,strict,expected', [
+    ([], True, {}),
+    pytest.mark.xfail(
+        ([{}], True, 'N/A'),
+        raises=counts.UnknownPrintingError),
+    ([{'id': TEST_PRINT_ID}], True, {}),
+    ([{'id': TEST_PRINT_ID, 'copies': 0, 'foils': 0}], True, {}),
+    ([{'id': TEST_PRINT_ID, 'copies': 1, 'foils': 2}], True, {
+        TEST_PRINT_ID: {
             counts.CountTypes.copies: 1,
             counts.CountTypes.foils: 2,
-        }
-    }
-
-
-def test_apc_with_find(cdb):
-    print_ = cdb.id_to_printing[
-        '536d407161fa03eddee7da0e823c2042a8fa0262']
-    card_counts = [{'set': 'S00', 'name': 'Rhox', 'copies': 1}]
-    print_counts = counts.aggregate_print_counts(cdb, card_counts)
-    assert print_counts == {
-        print_: {counts.CountTypes.copies: 1}
-    }
-
-
-def test_apc_multiple(cdb):
-    print1 = cdb.id_to_printing[TEST_PRINT_ID]
-    print2 = cdb.id_to_printing[
-        '536d407161fa03eddee7da0e823c2042a8fa0262']
-    card_counts = [
-        {'id': TEST_PRINT_ID, 'copies': 1, 'foils': 2},
-        {'set': 'S00', 'name': 'Rhox', 'copies': 1},
-    ]
-    print_counts = counts.aggregate_print_counts(cdb, card_counts)
-    assert print_counts == {
-        print1: {
+        }}),
+    ([{'set': 'S00', 'name': 'Rhox', 'copies': 1}], True, {
+        '536d407161fa03eddee7da0e823c2042a8fa0262': {
             counts.CountTypes.copies: 1,
-            counts.CountTypes.foils: 2,
-        },
-        print2: {counts.CountTypes.copies: 1},
-    }
-
-
-def test_apc_repeat(cdb):
-    print_ = cdb.id_to_printing[TEST_PRINT_ID]
-    card_counts = [
-        {'id': TEST_PRINT_ID, 'copies': 4},
-        {'id': TEST_PRINT_ID, 'copies': 3, 'foils': '8'},
-    ]
-    print_counts = counts.aggregate_print_counts(cdb, card_counts)
-    assert print_counts == {
-        print_: {
-            counts.CountTypes.copies: 7,
-            counts.CountTypes.foils: 8,
-        }
-    }
+        }}),
+    ([{'id': TEST_PRINT_ID, 'copies': 1, 'foils': 2},
+      {'set': 'S00', 'name': 'Rhox', 'copies': 1}],
+     True,
+     {TEST_PRINT_ID: {
+         counts.CountTypes.copies: 1,
+         counts.CountTypes.foils: 2},
+      '536d407161fa03eddee7da0e823c2042a8fa0262': {
+          counts.CountTypes.copies: 1}}),
+    ([{'id': TEST_PRINT_ID, 'copies': 4},
+      {'id': TEST_PRINT_ID, 'copies': 3, 'foils': '8'}],
+     True,
+     {TEST_PRINT_ID: {
+         counts.CountTypes.copies: 7,
+         counts.CountTypes.foils: 8}}),
+    ([{'set': 'LEA', 'name': 'Forest', 'copies': 1}], False, {
+        '5ede9781b0c5d157c28a15c3153a455d7d6180fa': {
+            counts.CountTypes.copies: 1}}),
+    pytest.mark.xfail(
+        ([{'set': 'LEA', 'name': 'Forest', 'copies': 1}], True, {
+            '5ede9781b0c5d157c28a15c3153a455d7d6180fa': {
+                counts.CountTypes.copies: 1}}),
+        raises=counts.UnknownPrintingError),
+])
+def test_aggregate_print_counts(cdb, card_rows, strict, expected):
+    print_counts = counts.aggregate_print_counts(cdb, card_rows, strict)
+    assert print_counts == expected
 
 
 @pytest.mark.parametrize('in_print_counts,out_print_counts', [
diff --git a/tests/mtg/test_models.py b/tests/mtg/test_models.py
index ff8a8e8..d21d683 100644
--- a/tests/mtg/test_models.py
+++ b/tests/mtg/test_models.py
@@ -6,13 +6,17 @@
 
 from mtg_ssm.mtg import models
 
-CARD_DB_SENTINEL = object()
+
+class Sentinel:
+    """Simple sentinel object class."""
+
+CARD_DB_SENTINEL = Sentinel()
 
 
 def test_card(cards_data):
     ag_card_data = cards_data['958ae1416f8f6287115ccd7c5c61f2415a313546']
     card = models.Card(CARD_DB_SENTINEL, ag_card_data)
-    assert card.cdb is CARD_DB_SENTINEL
+    assert card.cdb == CARD_DB_SENTINEL
     assert card.name == 'Abattoir Ghoul'
     assert not card.strict_basic
 
@@ -32,7 +36,7 @@ def test_card_strict_basic(cards_data, name, id_, strict_basic):
 def test_card_printing(cards_data):
     ag_card_data = cards_data['958ae1416f8f6287115ccd7c5c61f2415a313546']
     printing = models.CardPrinting(CARD_DB_SENTINEL, 'ISD', ag_card_data)
-    assert printing.cdb is CARD_DB_SENTINEL
+    assert printing.cdb == CARD_DB_SENTINEL
     assert printing.id_ == '958ae1416f8f6287115ccd7c5c61f2415a313546'
     assert printing.card_name == 'Abattoir Ghoul'
     assert printing.set_code == 'ISD'
@@ -64,7 +68,7 @@ def test_card_set(sets_data):
     # Execute
     card_set = models.CardSet(CARD_DB_SENTINEL, set_data)
     # Verify
-    assert card_set.cdb is CARD_DB_SENTINEL
+    assert card_set.cdb == CARD_DB_SENTINEL
     assert card_set.code == 'PLS'
     assert card_set.name == 'Planeshift'
     assert card_set.block == 'Invasion'
diff --git a/tests/serialization/test_csv.py b/tests/serialization/test_csv.py
index f41e316..eacf568 100644
--- a/tests/serialization/test_csv.py
+++ b/tests/serialization/test_csv.py
@@ -19,12 +19,6 @@ def cdb(sets_data):
     return card_db.CardDb(sets_data)
 
 
-@pytest.fixture
-def printing(cdb):
-    """Printing fixture for testing."""
-    return cdb.id_to_printing[TEST_PRINT_ID]
-
-
 def test_header():
     assert csv.CSV_HEADER == [
         'set',
@@ -37,7 +31,8 @@ def test_header():
     ]
 
 
-def test_row_for_printing(printing):
+def test_row_for_printing(cdb):
+    printing = cdb.id_to_printing[TEST_PRINT_ID]
     print_counts = {
         counts.CountTypes.copies: 3,
         counts.CountTypes.foils: 5,
@@ -54,8 +49,8 @@ def test_row_for_printing(printing):
     }
 
 
-def test_rows_for_printings_verbose(cdb, printing):
-    print_counts = {printing: {counts.CountTypes.copies: 3}}
+def test_rows_for_printings_verbose(cdb):
+    print_counts = {TEST_PRINT_ID: {counts.CountTypes.copies: 3}}
     rows = csv.rows_for_printings(cdb, print_counts, True)
     assert list(rows) == [
         {
@@ -76,8 +71,8 @@ def test_rows_for_printings_verbose(cdb, printing):
     ]
 
 
-def test_rows_for_printings_terse(cdb, printing):
-    print_counts = {printing: {counts.CountTypes.copies: 3}}
+def test_rows_for_printings_terse(cdb):
+    print_counts = {TEST_PRINT_ID: {counts.CountTypes.copies: 3}}
     rows = csv.rows_for_printings(cdb, print_counts, False)
     assert list(rows) == [
         {
@@ -91,8 +86,8 @@ def test_rows_for_printings_terse(cdb, printing):
     ]
 
 
-def test_write_verbose(cdb, printing):
-    print_counts = {printing: {
+def test_write_verbose(cdb):
+    print_counts = {TEST_PRINT_ID: {
         counts.CountTypes.copies: 1,
         counts.CountTypes.foils: 12,
     }}
@@ -107,8 +102,8 @@ def test_write_verbose(cdb, printing):
     """)
 
 
-def test_write_terse(cdb, printing):
-    print_counts = {printing: {
+def test_write_terse(cdb):
+    print_counts = {TEST_PRINT_ID: {
         counts.CountTypes.copies: 1,
         counts.CountTypes.foils: 12,
     }}
@@ -122,7 +117,7 @@ def test_write_terse(cdb, printing):
     """)
 
 
-def test_read(cdb, printing):
+def test_read(cdb):
     with tempfile.NamedTemporaryFile('w') as infile:
         infile.write(textwrap.dedent("""\
             set,name,number,multiverseid,id,copies,foils
@@ -131,7 +126,7 @@ def test_read(cdb, printing):
         infile.flush()
         serializer = csv.CsvFullDialect(cdb)
         print_counts = serializer.read(infile.name)
-    assert print_counts == {printing: {
+    assert print_counts == {TEST_PRINT_ID: {
         counts.CountTypes.copies: 3,
         counts.CountTypes.foils: 72,
     }}
diff --git a/tests/serialization/test_deckbox.py b/tests/serialization/test_deckbox.py
index 296a92a..cd0cf83 100644
--- a/tests/serialization/test_deckbox.py
+++ b/tests/serialization/test_deckbox.py
@@ -43,8 +43,9 @@ def test_get_deckbox_name(cdb):
 
 def test_rfp(cdb):
     # Setup
-    printing = cdb.id_to_printing['c08c564300a6a6d3f9c1c1dfbcab9351be3a04ae']
-    print_counts = {printing: {
+    print_id = 'c08c564300a6a6d3f9c1c1dfbcab9351be3a04ae'
+    printing = cdb.id_to_printing[print_id]
+    print_counts = {print_id: {
         counts.CountTypes.copies: 3,
         counts.CountTypes.foils: 5,
     }}
@@ -88,8 +89,9 @@ def test_rfp(cdb):
 
 
 def test_rfp_split_second_half(cdb):
-    printing = cdb.id_to_printing['2eecf5001fe332f5dadf4d87665bcf182c5f24ee']
-    print_counts = {printing: {
+    print_id = '2eecf5001fe332f5dadf4d87665bcf182c5f24ee'
+    printing = cdb.id_to_printing[print_id]
+    print_counts = {print_id: {
         counts.CountTypes.copies: 3,
         counts.CountTypes.foils: 5,
     }}
@@ -98,8 +100,9 @@ def test_rfp_split_second_half(cdb):
 
 
 def test_rfp_promo(cdb):
-    printing = cdb.id_to_printing['6c9ffa9ffd2cf7e6f85c6be1713ee0c546b9f8fc']
-    print_counts = {printing: {
+    print_id = '6c9ffa9ffd2cf7e6f85c6be1713ee0c546b9f8fc'
+    printing = cdb.id_to_printing[print_id]
+    print_counts = {print_id: {
         counts.CountTypes.copies: 0,
         counts.CountTypes.foils: 5,
     }}
@@ -125,7 +128,7 @@ def test_rfp_promo(cdb):
     ]
 
 
-@pytest.mark.xfail(strict=True)
+@pytest.mark.xfail
 def test_alt_art_ertai(cdb):
     ertai1 = cdb.id_to_printing['08fcfee6a7c4eddcd44e43e918cbf9d479492fe7']
     ertai2 = cdb.id_to_printing['62ff415cafefac84a5bb7174cb7ef175c14625de']
@@ -139,19 +142,16 @@ def test_alt_art_ertai(cdb):
 
 
 def test_rows_from_print_counts(cdb):
-    bust = cdb.id_to_printing['2eecf5001fe332f5dadf4d87665bcf182c5f24ee']
-    boom = cdb.id_to_printing['c08c564300a6a6d3f9c1c1dfbcab9351be3a04ae']
-    bsz = cdb.id_to_printing['6c9ffa9ffd2cf7e6f85c6be1713ee0c546b9f8fc']
     print_counts = {
-        bust: {
+        '2eecf5001fe332f5dadf4d87665bcf182c5f24ee': {
             counts.CountTypes.copies: 3,
             counts.CountTypes.foils: 5,
         },
-        boom: {
+        'c08c564300a6a6d3f9c1c1dfbcab9351be3a04ae': {
             counts.CountTypes.copies: 7,
             counts.CountTypes.foils: 9,
         },
-        bsz: {
+        '6c9ffa9ffd2cf7e6f85c6be1713ee0c546b9f8fc': {
             counts.CountTypes.foils: 11,
         }
     }
@@ -241,11 +241,11 @@ def test_create_counts_row(cdb, deckbox_row, target_card_row):
 
 def test_write(cdb):
     # Setup
-    boom = cdb.id_to_printing['c08c564300a6a6d3f9c1c1dfbcab9351be3a04ae']
-    bsz = cdb.id_to_printing['6c9ffa9ffd2cf7e6f85c6be1713ee0c546b9f8fc']
     print_counts = {
-        boom: {counts.CountTypes.copies: 1},
-        bsz: {counts.CountTypes.foils: 3},
+        'c08c564300a6a6d3f9c1c1dfbcab9351be3a04ae': {
+            counts.CountTypes.copies: 1},
+        '6c9ffa9ffd2cf7e6f85c6be1713ee0c546b9f8fc': {
+            counts.CountTypes.foils: 3},
     }
     serializer = deckbox.DeckboxCsvDialect(cdb)
     with tempfile.NamedTemporaryFile(mode='rt') as outfile:
@@ -269,9 +269,9 @@ def test_read(cdb):
         infile.flush()
         serializer = deckbox.DeckboxCsvDialect(cdb)
         print_counts = serializer.read(infile.name)
-    boom = cdb.id_to_printing['c08c564300a6a6d3f9c1c1dfbcab9351be3a04ae']
-    bsz = cdb.id_to_printing['6c9ffa9ffd2cf7e6f85c6be1713ee0c546b9f8fc']
     assert print_counts == {
-        boom: {counts.CountTypes.copies: 5},
-        bsz: {counts.CountTypes.foils: 11},
+        'c08c564300a6a6d3f9c1c1dfbcab9351be3a04ae': {
+            counts.CountTypes.copies: 5},
+        '6c9ffa9ffd2cf7e6f85c6be1713ee0c546b9f8fc': {
+            counts.CountTypes.foils: 11},
     }
diff --git a/tests/serialization/test_xlsx.py b/tests/serialization/test_xlsx.py
index 56c986d..91ef6a2 100644
--- a/tests/serialization/test_xlsx.py
+++ b/tests/serialization/test_xlsx.py
@@ -97,16 +97,12 @@ def test_create_all_cards_sheet(cdb):
 
 
 def test_create_set_sheet(cdb):
-    forest1 = cdb.id_to_printing[
-        '676a1f5b64dc03bbb3876840c3ff2ba2c16f99cb']
-    forest2 = cdb.id_to_printing[
-        'd0a4414893bc2f9bd3beea2f8f2693635ef926a4']
-    forest3 = cdb.id_to_printing[
-        'c78d2da78c68c558b1adc734b3f164e885407ffc']
     print_counts = {
-        forest1: {counts.CountTypes.copies: 1},
-        forest2: {counts.CountTypes.foils: 2},
-        forest3: {
+        '676a1f5b64dc03bbb3876840c3ff2ba2c16f99cb': {
+            counts.CountTypes.copies: 1},
+        'd0a4414893bc2f9bd3beea2f8f2693635ef926a4': {
+            counts.CountTypes.foils: 2},
+        'c78d2da78c68c558b1adc734b3f164e885407ffc': {
             counts.CountTypes.copies: 3,
             counts.CountTypes.foils: 4,
         }
@@ -130,7 +126,7 @@ def test_create_set_sheet(cdb):
 
 def test_write(cdb):
     print_counts = {
-        cdb.id_to_printing['536d407161fa03eddee7da0e823c2042a8fa0262']: {
+        '536d407161fa03eddee7da0e823c2042a8fa0262': {
             counts.CountTypes.copies: 7,
             counts.CountTypes.foils: 12,
         }
@@ -182,7 +178,7 @@ def test_read_from_file(cdb):
         workbook.save(infile.name)
         print_counts = serializer.read(infile.name)
     assert print_counts == {
-        cdb.id_to_printing['536d407161fa03eddee7da0e823c2042a8fa0262']: {
+        '536d407161fa03eddee7da0e823c2042a8fa0262': {
             counts.CountTypes.copies: 3,
             counts.CountTypes.foils: 7,
         }
diff --git a/tests/test_ssm.py b/tests/test_ssm.py
index 1ed99b6..ed1c4f6 100644
--- a/tests/test_ssm.py
+++ b/tests/test_ssm.py
@@ -144,11 +144,12 @@ def test_update_cmd():
         ssm.update_cmd(args)
         assert set(os.listdir(tmpdirname)) == {
             'infile.csv',
-            'infile.csv.bak-20150628_000000',
+            'infile.20150628_000000.csv',
         }
         with open(infilename, 'rt') as outfile:
             outfiledata = outfile.read()
-        with open(infilename + '.bak-20150628_000000') as bakfile:
+        bakfilename = os.path.join(tmpdirname, 'infile.20150628_000000.csv')
+        with open(bakfilename) as bakfile:
             bakfiledata = bakfile.read()
     assert outfiledata == textwrap.dedent("""\
         set,name,number,multiverseid,id,copies,foils
@@ -214,13 +215,14 @@ def test_merge_cmd_existing():
         assert set(os.listdir(tmpdirname)) == {
             'import.csv',
             'outfile.csv',
-            'outfile.csv.bak-20150628_000000',
+            'outfile.20150628_000000.csv',
         }
         with open(outfilename, 'rt') as outfile:
             outfiledata = outfile.read()
         with open(importname, 'rt') as importfile:
             importdata = importfile.read()
-        with open(outfilename + '.bak-20150628_000000') as bakfile:
+        bakfilename = os.path.join(tmpdirname, 'outfile.20150628_000000.csv')
+        with open(bakfilename) as bakfile:
             bakfiledata = bakfile.read()
     assert outfiledata == textwrap.dedent("""\
         set,name,number,multiverseid,id,copies,foils