diff --git a/cdc/store_test.go b/cdc/store_test.go
index bbde0a3..a423fd1 100644
--- a/cdc/store_test.go
+++ b/cdc/store_test.go
@@ -113,8 +113,10 @@ func TestRead(t *testing.T) {
 func TestWriteSuccess(t *testing.T) {
 	cdcs := setup(t, "", cdc.NoRetryPolicy)
 
+	// Note we don't explicitly set ID here, so that MongoDB will generate an _id for us.
+	// This is the same behavior as the actual store implementation, which does not set the _id and
+	// allows MongoDB to generate it.
 	event := etre.CDCEvent{
-		Id:         "abc",
 		Ts:         54,
 		Op:         "i",
 		Caller:     "mike",
@@ -140,6 +142,19 @@ func TestWriteSuccess(t *testing.T) {
 	actualEvents, err := cdcs.Read(filter)
 	require.NoError(t, err)
 	assert.Len(t, actualEvents, 1)
+
+	// MongoDB auto-generates the _id column since we didn't provide one in `event` above.
+	// This is the same behavior as the actual store implementation, which does not set the _id and
+	// allows MongoDB to generate it.
+	//
+	// Since we don't know what the generated _id will be, we can't compare the entire event directly.
+	// Instead, verify that the _id is a valid ObjectID and then clear it so we can compare the rest
+	// of the event we read (in actualEvents[0]) with the original `event` above.
+	_, err = bson.ObjectIDFromHex(actualEvents[0].Id)
+	require.NoError(t, err)
+	actualEvents[0].Id = ""
+
+	// Compare the rest of the event
 	assert.Equal(t, event, actualEvents[0])
 }
 
diff --git a/server/server.go b/server/server.go
index 2a0fe00..1737475 100644
--- a/server/server.go
+++ b/server/server.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"go.mongodb.org/mongo-driver/v2/mongo"
+	"go.mongodb.org/mongo-driver/v2/mongo/options"
 
 	"github.com/square/etre"
 	"github.com/square/etre/api"
@@ -64,7 +65,8 @@ func (s *Server) Boot(configFile string) error {
 			return fmt.Errorf("cannot connect to CDC datasource: %s", err)
 		}
 		s.cdcDbClient = cdcClient
-		cdcColl := cdcClient.Database(cfg.Datasource.Database).Collection(config.CDC_COLLECTION)
+		cdcOpts := options.Collection().SetBSONOptions(&options.BSONOptions{ObjectIDAsHexString: true}) // Because etre.CDCEvent has string _id, not bson.ObjectID
+		cdcColl := cdcClient.Database(cfg.Datasource.Database).Collection(config.CDC_COLLECTION, cdcOpts)
 
 		// Store
 		wrp := cdc.RetryPolicy{
diff --git a/test/db.go b/test/db.go
index f5cc523..b8f4a40 100644
--- a/test/db.go
+++ b/test/db.go
@@ -24,7 +24,12 @@ func DbCollections(entityTypes []string) (*mongo.Client, map[string]*mongo.Colle
 	}
 	coll := map[string]*mongo.Collection{}
 	for _, t := range entityTypes {
-		coll[t] = client.Database(database).Collection(t)
+		if t == "cdc" {
+			cdcOpts := options.Collection().SetBSONOptions(&options.BSONOptions{ObjectIDAsHexString: true}) // Because etre.CDCEvent has string _id, not bson.ObjectID
+			coll[t] = client.Database(database).Collection(t, cdcOpts)
+		} else {
+			coll[t] = client.Database(database).Collection(t)
+		}
 	}
 	return client, coll, nil
 }