diff --git a/market/ws/delta_validation_test.go b/market/ws/delta_validation_test.go
new file mode 100644
index 00000000..f4d0b4b0
--- /dev/null
+++ b/market/ws/delta_validation_test.go
@@ -0,0 +1,131 @@
+# Fix for Issue #4: [$45 BOUNTY] [Go] Add WebSocket order book delta validation tests
+
+// market/ws/test_helpers.go
+package ws
+
+import (
+	"encoding/json"
+	"errors"
+	"sync"
+)
+
+// MockWebSocketConn provides a deterministic WebSocket connection for testing
+type MockWebSocketConn struct {
+	mu           sync.Mutex
+	messages     [][]byte
+	messageIndex int
+	closed       bool
+	writeBuffer  [][]byte
+}
+
+// NewMockWebSocketConn creates a new mock connection with predefined messages
+func NewMockWebSocketConn(messages [][]byte) *MockWebSocketConn {
+	return &MockWebSocketConn{
+		messages:     messages,
+		messageIndex: 0,
+		writeBuffer:  make([][]byte, 0),
+	}
+}
+
+// ReadMessage returns the next predefined message
+func (m *MockWebSocketConn) ReadMessage() (messageType int, p []byte, err error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if m.closed {
+		return 0, nil, errors.New("connection closed")
+	}
+
+	if m.messageIndex >= len(m.messages) {
+		return 0, nil, errors.New("no more messages")
+	}
+
+	msg := m.messages[m.messageIndex]
+	m.messageIndex++
+	return 1, msg, nil // 1 = TextMessage
+}
+
+// WriteMessage stores the message in the write buffer
+func (m *MockWebSocketConn) WriteMessage(messageType int, data []byte) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if m.closed {
+		return errors.New("connection closed")
+	}
+
+	m.writeBuffer = append(m.writeBuffer, data)
+	return nil
+}
+
+// Close marks the connection as closed
+func (m *MockWebSocketConn) Close() error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.closed = true
+	return nil
+}
+
+// GetWrittenMessages returns all messages written to the connection
+func (m *MockWebSocketConn) GetWrittenMessages() [][]byte {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	return m.writeBuffer
+}
+
+// OrderBookDelta represents a delta update to the order book
+type OrderBookDelta struct {
+	Type      string          `json:"type"`
+	Symbol    string          `json:"symbol"`
+	Sequence  int64           `json:"sequence"`
+	Bids      [][]interface{} `json:"bids,omitempty"`
+	Asks      [][]interface{} `json:"asks,omitempty"`
+	Timestamp int64           `json:"timestamp"`
+	Checksum  string          `json:"checksum,omitempty"`
+}
+
+// OrderBookSnapshot represents a full order book snapshot
+type OrderBookSnapshot struct {
+	Type      string          `json:"type"`
+	Symbol    string          `json:"symbol"`
+	Sequence  int64           `json:"sequence"`
+	Bids      [][]interface{} `json:"bids"`
+	Asks      [][]interface{} `json:"asks"`
+	Timestamp int64           `json:"timestamp"`
+	Checksum  string          `json:"checksum,omitempty"`
+}
+
+// CreateDeltaMessage creates a JSON-encoded delta message
+func CreateDeltaMessage(delta OrderBookDelta) []byte {
+	data, _ := json.Marshal(delta)
+	return data
+}
+
+// CreateSnapshotMessage creates a JSON-encoded snapshot message
+func CreateSnapshotMessage(snapshot OrderBookSnapshot) []byte {
+	data, _ := json.Marshal(snapshot)
+	return data
+}
+
+// DeltaValidationError represents a validation error for delta processing
+type DeltaValidationError struct {
+	Code    string `json:"code"`
+	Message string `json:"message"`
+	Field   string `json:"field,omitempty"`
+}
+
+func (e *DeltaValidationError) Error() string {
+	return e.Message
+}
+
+// ValidationErrorCodes for delta validation
+const (
+	ErrCodeMalformedPrice    = "MALFORMED_PRICE"
+	ErrCodeMalformedQuantity = "MALFORMED_QUANTITY"
+	ErrCodeMalformedSide     = "MALFORMED_SIDE"
+	ErrCodeMalformedSymbol   = "MALFORMED_SYMBOL"
+	ErrCodeStaleSequence     = "STALE_SEQUENCE"
+	ErrCodeOutOfOrder        = "OUT_OF_ORDER_SEQUENCE"
+	ErrCodeChecksumMismatch  = "CHECKSUM_MISMATCH"
+	ErrCodeInvalidPayload    = "INVALID_PAYLOAD"
+)
\ No newline at end of file