diff --git a/tests/test_meta_invoice.py b/tests/test_meta_invoice.py
index 88ed46bdc897797282f39f03e4544c46de48abf7..7de49c5016799d6a08c4aa3887d0ba290ebd9d06 100644
--- a/tests/test_meta_invoice.py
+++ b/tests/test_meta_invoice.py
@@ -37,6 +37,9 @@ NON_REQUIRED_ACCOUNTS = {
 
 TEST_KEY = 'invoice'
 
+MISSING_MSG = f'{{}} missing {TEST_KEY}'.format
+WRONG_TYPE_MSG = f'{{}} has wrong type of {TEST_KEY}: expected str but is a {{}}'.format
+
 @pytest.fixture(scope='module')
 def hook():
     config = testutil.TestConfig()
@@ -77,13 +80,12 @@ def test_bad_type_values_on_postings(hook, acct1, acct2, value):
         (acct2, -25),
         (acct1, 25, {TEST_KEY: value}),
     ])
-    expected_msg = "{} has wrong type of {}: expected str but is a {}".format(
-        acct1,
-        TEST_KEY,
-        type(value).__name__,
-    )
+    expected = {
+        MISSING_MSG(acct1),
+        WRONG_TYPE_MSG(acct1, type(value).__name__),
+    }
     actual = {error.message for error in hook.run(txn)}
-    assert actual == {expected_msg}
+    assert actual == expected
 
 @pytest.mark.parametrize('acct1,acct2,value', testutil.combine_values(
     REQUIRED_ACCOUNTS,
@@ -120,13 +122,12 @@ def test_bad_type_values_on_transaction(hook, acct1, acct2, value):
         (acct2, -25),
         (acct1, 25),
     ])
-    expected_msg = "{} has wrong type of {}: expected str but is a {}".format(
-        acct1,
-        TEST_KEY,
-        type(value).__name__,
-    )
+    expected = {
+        MISSING_MSG(acct1),
+        WRONG_TYPE_MSG(acct1, type(value).__name__),
+    }
     actual = {error.message for error in hook.run(txn)}
-    assert actual == {expected_msg}
+    assert actual == expected
 
 @pytest.mark.parametrize('acct1,acct2', testutil.combine_values(
     REQUIRED_ACCOUNTS,