diff --git a/src/_zkapauthorizer/tests/fixtures.py b/src/_zkapauthorizer/tests/fixtures.py
index 35aadaea07c79020433806bdcf6ccea6cb2e4410..1b226500bc327358f4dfa3ee28b981b209ca9d88 100644
--- a/src/_zkapauthorizer/tests/fixtures.py
+++ b/src/_zkapauthorizer/tests/fixtures.py
@@ -20,6 +20,10 @@ from __future__ import (
     absolute_import,
 )
 
+from base64 import (
+    b64encode,
+)
+
 import attr
 
 from fixtures import (
@@ -43,6 +47,7 @@ from ..model import (
     memory_connect,
 )
 from ..controller import (
+    DummyRedeemer,
     PaymentController,
 )
 
@@ -99,8 +104,12 @@ class ConfiglessMemoryVoucherStore(Fixture):
     This is like ``TemporaryVoucherStore`` but faster because it skips the
     Tahoe-LAFS parts.
     """
-    redeemer = attr.ib()
     get_now = attr.ib()
+    _public_key = attr.ib(default=b64encode(b"A" * 32).decode("utf-8"))
+    redeemer = attr.ib(default=None, init=False)
+
+    def __attrs_post_init__(self):
+        self.redeemer = DummyRedeemer(self._public_key)
 
     def _setUp(self):
         here = FilePath(u".")
diff --git a/src/_zkapauthorizer/tests/test_model.py b/src/_zkapauthorizer/tests/test_model.py
index 46a794e7f99d09f151ebd876242ce831a1ebb11c..039dcffe7901223c5dc5040359498299deccb2b1 100644
--- a/src/_zkapauthorizer/tests/test_model.py
+++ b/src/_zkapauthorizer/tests/test_model.py
@@ -425,9 +425,7 @@ class UnblindedTokenStateMachine(RuleBasedStateMachine):
     def __init__(self, case):
         super(UnblindedTokenStateMachine, self).__init__()
         self.case = case
-        self.redeemer = DummyRedeemer()
         self.configless = ConfiglessMemoryVoucherStore(
-            self.redeemer,
             # Time probably not actually relevant to this state machine.
             datetime.now,
         )
diff --git a/src/_zkapauthorizer/tests/test_spending.py b/src/_zkapauthorizer/tests/test_spending.py
index e55f289a3936a709566101f2effe35fecb2855dc..1fc4e36fe0dc99045ab34e1d08c8885006b79f17 100644
--- a/src/_zkapauthorizer/tests/test_spending.py
+++ b/src/_zkapauthorizer/tests/test_spending.py
@@ -71,7 +71,6 @@ class PassGroupTests(TestCase):
         """
         configless = self.useFixture(
             ConfiglessMemoryVoucherStore(
-                DummyRedeemer(),
                 lambda: now,
             ),
         )
@@ -109,7 +108,6 @@ class PassGroupTests(TestCase):
     ):
         configless = self.useFixture(
             ConfiglessMemoryVoucherStore(
-                DummyRedeemer(),
                 lambda: now,
             ),
         )