diff --git a/errors.go b/errors.go
index dec7382..a211bfc 100644
--- a/errors.go
+++ b/errors.go
@@ -26,7 +26,7 @@ var (
 	cancelProto   = status.FromContextError(context.Canceled).Proto()
 	deadlineProto = status.FromContextError(context.DeadlineExceeded).Proto()
 
-	filterErr = errors.New(filterErrMsg)
+	filterErr = errors.New(filterErrMsg, j.C("ERR_d5e8f7a9b2c3d4e5"))
 )
 
 // IsStoppedErr checks whether err is an ErrStopped
@@ -60,5 +60,5 @@ func IsFilterErr(err error) bool {
 }
 
 func asFilterErr(err error) error {
-	return errors.Wrap(err, filterErrMsg)
+	return errors.Wrap(err, filterErrMsg, j.C("ERR_d5e8f7a9b2c3d4e5"))
 }
diff --git a/filters/metadata.go b/filters/metadata.go
index fe8ab72..0917a7c 100644
--- a/filters/metadata.go
+++ b/filters/metadata.go
@@ -18,8 +18,8 @@ const (
 )
 
 var (
-	metadataEventFilterErr = errors.New(metadataEventFilterErrMsg)
-	deserializationErr     = errors.New(deserializationErrMsg)
+	metadataEventFilterErr = errors.New(metadataEventFilterErrMsg, j.C("ERR_c1f2e3d4a5b6c7d8"))
+	deserializationErr     = errors.New(deserializationErrMsg, j.C("ERR_a1b2c3d4e5f6a7b8"))
 )
 
 func MetadataEventFilter[T any](ds Deserializer[T], flt DataFilter[T]) (reflex.EventFilter, error) {
@@ -45,7 +45,7 @@ func IsDeserializationErr(err error) bool {
 }
 
 func asDeserializationErr(err error) error {
-	return errors.Wrap(err, deserializationErrMsg)
+	return errors.Wrap(err, deserializationErrMsg, j.C("ERR_a1b2c3d4e5f6a7b8"))
 }
 
 // IsMetadataEventFilterErr returns true if the error occurred during construction of a MetadataEventFilter.
@@ -54,5 +54,6 @@ func IsMetadataEventFilterErr(err error) bool {
 }
 
 func makeMetadataEventFilterErr(ol ...errors.Option) error {
-	return errors.New(metadataEventFilterErrMsg, ol...)
+	opts := append([]errors.Option{j.C("ERR_c1f2e3d4a5b6c7d8")}, ol...)
+	return errors.New(metadataEventFilterErrMsg, opts...)
 }
diff --git a/filters/metadata_test.go b/filters/metadata_test.go
index 3b8cc9f..34fdee4 100644
--- a/filters/metadata_test.go
+++ b/filters/metadata_test.go
@@ -4,12 +4,18 @@ import (
 	"testing"
 
 	"github.com/luno/jettison/errors"
+	"github.com/luno/jettison/j"
 	"github.com/luno/jettison/jtest"
 	"github.com/stretchr/testify/require"
 
 	"github.com/luno/reflex"
 )
 
+var (
+	testBadMetadataErr = errors.New("bad metadata", j.C("ERR_test_bad_metadata"))
+	testBadFilterErr   = errors.New("bad filter", j.C("ERR_test_bad_filter"))
+)
+
 func TestMakeMetadataEventFilter(t *testing.T) {
 	type testCase struct {
 		name string
@@ -74,12 +80,12 @@ func TestMetadataEventFilter(t *testing.T) {
 			name: "Deserializer errors",
 			e:    &reflex.Event{MetaData: m},
 			ds: func(x *testing.T) Deserializer[string] {
-				return func(b []byte) (string, error) { require.Equal(x, m, b); return string(b), errors.New("bad metadata") }
+				return func(b []byte) (string, error) { require.Equal(x, m, b); return string(b), testBadMetadataErr }
 			},
 			flt: func(x *testing.T) DataFilter[string] {
 				return func(s string) (bool, error) { require.Fail(x, "should not be reached"); return true, nil }
 			},
-			err: []error{deserializationErr, errors.New("bad metadata")},
+			err: []error{deserializationErr, testBadMetadataErr},
 		},
 		{
 			name: "Data Filter errors",
@@ -88,9 +94,9 @@ func TestMetadataEventFilter(t *testing.T) {
 				return func(b []byte) (string, error) { require.Equal(x, m, b); return string(b), nil }
 			},
 			flt: func(x *testing.T) DataFilter[string] {
-				return func(s string) (bool, error) { require.Equal(x, d, s); return true, errors.New("bad filter") }
+				return func(s string) (bool, error) { require.Equal(x, d, s); return true, testBadFilterErr }
 			},
-			err: []error{errors.New("bad filter")},
+			err: []error{testBadFilterErr},
 		},
 		{
 			name: "Exclude",
@@ -159,7 +165,7 @@ func TestIsDeserializationErr(t *testing.T) {
 		{
 			name: "constructed deserialization error",
 			err:  errors.New(deserializationErrMsg),
-			want: true,
+			want: false,
 		},
 	}
 	for _, tt := range tests {
diff --git a/rpatterns/batch.go b/rpatterns/batch.go
index f507da2..415831c 100644
--- a/rpatterns/batch.go
+++ b/rpatterns/batch.go
@@ -22,7 +22,10 @@ type batchEvent struct {
 
 const minWait = time.Millisecond * 100
 
-var ErrBatchState = errors.New("batch error state", j.C("ERR_b3053f5f1a3ecd23"))
+var (
+	ErrBatchState      = errors.New("batch error state", j.C("ERR_b3053f5f1a3ecd23"))
+	ErrInvalidBatchConfig = errors.New("batchPeriod or batchLen must be non-zero", j.C("ERR_invalid_batch_config"))
+)
 
 // BatchConsumer provides a reflex consumer that buffers events
 // and flushes a batch to the consume function when either
@@ -95,7 +98,7 @@ func (c *BatchConsumer) Stop() error {
 // enqueue adds the event to the buffer or returns error if batch needs to be reset.
 func (c *BatchConsumer) enqueue(ctx context.Context, e *AckEvent) error {
 	if c.flushPeriod == 0 && c.flushLen == 0 {
-		return errors.New("batchPeriod or batchLen must be non-zero")
+		return ErrInvalidBatchConfig
 	}
 
 	// Add event to batch queue
diff --git a/rpatterns/batch_test.go b/rpatterns/batch_test.go
index 3853001..6971d2c 100644
--- a/rpatterns/batch_test.go
+++ b/rpatterns/batch_test.go
@@ -105,7 +105,6 @@ func TestRunBatchConsumer(t *testing.T) {
 }
 
 func TestReset(t *testing.T) {
-	recvEndErr := errors.New("recv error")
 	tests := []struct {
 		name       string
 		batchLen   int
@@ -146,13 +145,13 @@ func TestReset(t *testing.T) {
 			spec := rpatterns.NewBatchSpec(b.Stream, consumer)
 			ctx := context.Background()
 			err := reflex.Run(ctx, spec)
-			jtest.Assert(t, recvEndErr, err)
+			jtest.Assert(t, errEvents, err)
 
 			events = ItoEList(tt.passEvents...)
 			b.events = events
 
 			err = reflex.Run(ctx, spec)
-			jtest.Assert(t, recvEndErr, err)
+			jtest.Assert(t, errEvents, err)
 		})
 	}
 }
@@ -171,7 +170,7 @@ func TestInvalidConfig(t *testing.T) {
 	spec := rpatterns.NewBatchSpec(b.Stream, consumer)
 	ctx := context.Background()
 	err := reflex.Run(ctx, spec)
-	jtest.Assert(t, errors.New("batchPeriod or batchLen must be non-zero"), err)
+	jtest.Assert(t, rpatterns.ErrInvalidBatchConfig, err)
 }
 
 type EventList struct {