diff --git a/core/transport/headers_test.go b/core/transport/headers_test.go
new file mode 100644
index 0000000..e84ac73
--- /dev/null
+++ b/core/transport/headers_test.go
@@ -0,0 +1,55 @@
+package transport
+
+import (
+	"net/http"
+	"reflect"
+	"testing"
+)
+
+func TestNewHeaders_NormalInput(t *testing.T) {
+	input := []string{"Content-Type=application/json", "Accept=*/*"}
+	want := http.Header{
+		"Content-Type": {"application/json"},
+		"Accept":       {"*/*"},
+	}
+	got := NewHeaders(input)
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("NewHeaders() = %v, want %v", got, want)
+	}
+}
+
+func TestNewHeaders_InvalidFormat(t *testing.T) {
+	input := []string{"invalid-header", "AnotherOne"}
+	want := http.Header{}
+	got := NewHeaders(input)
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("NewHeaders() = %v, want %v", got, want)
+	}
+}
+
+func TestNewHeaders_DuplicateKeys(t *testing.T) {
+	input := []string{"X-Test=1", "X-Test=2"}
+	want := http.Header{
+		"X-Test": {"1", "2"},
+	}
+	got := NewHeaders(input)
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("NewHeaders() = %v, want %v", got, want)
+	}
+}
+
+func TestNewHeaders_EmptyOrNilInput(t *testing.T) {
+	var inputNil []string
+	inputEmpty := []string{}
+	want := http.Header{}
+
+	gotNil := NewHeaders(inputNil)
+	if !reflect.DeepEqual(gotNil, want) {
+		t.Errorf("NewHeaders(nil) = %v, want %v", gotNil, want)
+	}
+
+	gotEmpty := NewHeaders(inputEmpty)
+	if !reflect.DeepEqual(gotEmpty, want) {
+		t.Errorf("NewHeaders(empty) = %v, want %v", gotEmpty, want)
+	}
+}
diff --git a/core/transport/transport_test.go b/core/transport/transport_test.go
new file mode 100644
index 0000000..7451699
--- /dev/null
+++ b/core/transport/transport_test.go
@@ -0,0 +1,128 @@
+package transport
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"reflect"
+	"testing"
+)
+
+// mockRoundTripper is used to intercept requests and record headers
+type mockRoundTripper struct {
+	lastReq *http.Request
+	resp    *http.Response
+	err     error
+}
+
+func (m *mockRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	m.lastReq = req
+	if m.resp != nil || m.err != nil {
+		return m.resp, m.err
+	}
+	return &http.Response{StatusCode: 200, Body: http.NoBody, Request: req}, nil
+}
+
+func TestDefaultHeaderTransport_CustomHeaders(t *testing.T) {
+	mock := &mockRoundTripper{}
+	tr := &DefaultHeaderTransport{
+		Origin: mock,
+		Header: http.Header{
+			"X-Test": {"abc"},
+			"Foo":    {"bar"},
+		},
+		AppName:    "myapp",
+		AppVersion: "1.2.3",
+	}
+	req, _ := http.NewRequestWithContext(context.Background(), "GET", "http://example.com", nil)
+	resp, err := tr.RoundTrip(req)
+	if err != nil {
+		t.Fatalf("RoundTrip error: %v", err)
+	}
+	if resp != nil && resp.Body != nil {
+		resp.Body.Close()
+	}
+
+	want := http.Header{
+		"X-Test":        {"abc"},
+		"Foo":           {"bar"},
+		"X-App-Name":    {"myapp"},
+		"X-App-Version": {"1.2.3"},
+	}
+	for k, v := range want {
+		got := req.Header.Values(k)
+		if !reflect.DeepEqual(got, v) {
+			t.Errorf("Header %q = %v, want %v", k, got, v)
+		}
+	}
+}
+
+func TestDefaultHeaderTransport_EmptyHeadersAndAppInfo(t *testing.T) {
+	mock := &mockRoundTripper{}
+	tr := &DefaultHeaderTransport{
+		Origin:     mock,
+		Header:     http.Header{},
+		AppName:    "",
+		AppVersion: "",
+	}
+	req, _ := http.NewRequestWithContext(context.Background(), "GET", "http://example.com", nil)
+	resp, err := tr.RoundTrip(req)
+	if err != nil {
+		t.Fatalf("RoundTrip error: %v", err)
+	}
+	if resp != nil && resp.Body != nil {
+		resp.Body.Close()
+	}
+
+	// x-app-name/version should not be present
+	if req.Header.Get("x-app-name") != "" {
+		t.Errorf("x-app-name should be empty")
+	}
+	if req.Header.Get("x-app-version") != "" {
+		t.Errorf("x-app-version should be empty")
+	}
+}
+
+func TestDefaultHeaderTransport_OriginErrorPropagation(t *testing.T) {
+	mock := &mockRoundTripper{err: errors.New("mock error")}
+	tr := &DefaultHeaderTransport{
+		Origin:     mock,
+		Header:     http.Header{},
+		AppName:    "",
+		AppVersion: "",
+	}
+	req, _ := http.NewRequestWithContext(context.Background(), "GET", "http://example.com", nil)
+	resp, err := tr.RoundTrip(req)
+	if resp != nil && resp.Body != nil {
+		resp.Body.Close()
+	}
+	if err == nil || err.Error() != "mock error" {
+		t.Errorf("Expected error 'mock error', got %v", err)
+	}
+}
+
+func TestDefaultHeaderTransport_MultipleHeaderValues(t *testing.T) {
+	mock := &mockRoundTripper{}
+	tr := &DefaultHeaderTransport{
+		Origin: mock,
+		Header: http.Header{
+			"X-Multi": {"a", "b"},
+		},
+		AppName:    "app",
+		AppVersion: "v",
+	}
+	req, _ := http.NewRequestWithContext(context.Background(), "GET", "http://example.com", nil)
+	resp, err := tr.RoundTrip(req)
+	if err != nil {
+		t.Fatalf("RoundTrip error: %v", err)
+	}
+	if resp != nil && resp.Body != nil {
+		resp.Body.Close()
+	}
+
+	got := req.Header.Values("X-Multi")
+	want := []string{"a", "b"}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("X-Multi header = %v, want %v", got, want)
+	}
+}