Add tests for pkg/cassandra/gocql/testutils (#5153)

**Which problem is this PR solving?**

This PR addresses a part of the issue
[#5068](#5068) by adding
tests for the `pkg/cassandra/gocql/testutils` package.

**Description of the changes**

The commit introduces tests for the `pkg/cassandra/gocql/testutils`
package to ensure the correctness of the User Defined Type (UDT)
functionality. These tests cover the `MarshalUDT` and `UnmarshalUDT`
methods of the `CustomUDT` type.

**How was this change tested?**

The changes were tested by running the following command:

```bash
make test
```

**Checklist**

- [x] I have read
[CONTRIBUTING_GUIDELINES.md](https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md)
- [x] I have signed all commits
- [x] I have added unit tests for the new functionality
- [x] I have run lint and test steps successfully
  - `for jaeger: make lint test`
  - `for jaeger-ui: yarn lint` and `yarn test`

---------

Signed-off-by: Wise-Wizard <saransh.shankar@gmail.com>

pkg/cassandra/gocql/testutils/udt_test.go

@@ -0,0 +1,81 @@
+// Copyright (c) 2024 The Jaeger Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package testutils_test
+
+import (
+	"testing"
+
+	"github.com/gocql/gocql"
+
+	"github.com/jaegertracing/jaeger/pkg/cassandra/gocql/testutils"
+)
+
+// CustomUDT is a custom type that implements gocql.UDTMarshaler and gocql.UDTUnmarshaler interfaces.
+type CustomUDT struct {
+	Field1 int
+	Field2 string
+}
+
+// MarshalUDT implements the gocql.UDTMarshaler interface.
+func (c *CustomUDT) MarshalUDT(name string, info gocql.TypeInfo) ([]byte, error) {
+	switch name {
+	case "Field1":
+		return gocql.Marshal(info, c.Field1)
+	case "Field2":
+		return gocql.Marshal(info, c.Field2)
+	default:
+		return nil, gocql.ErrNotFound
+	}
+}
+
+// UnmarshalUDT implements the gocql.UDTUnmarshaler interface.
+func (c *CustomUDT) UnmarshalUDT(name string, info gocql.TypeInfo, data []byte) error {
+	switch name {
+	case "Field1":
+		return gocql.Unmarshal(info, data, &c.Field1)
+	case "Field2":
+		return gocql.Unmarshal(info, data, &c.Field2)
+	default:
+		return gocql.ErrNotFound
+	}
+}
+
+func TestUDTTestCase(t *testing.T) {
+	udtInstance := &CustomUDT{
+		Field1: 1,
+		Field2: "test",
+	}
+
+	// Define UDT fields for testing
+	udtFields := []testutils.UDTField{
+		{
+			Name:  "Field1",
+			Type:  gocql.TypeBigInt,
+			ValIn: []byte{0, 0, 0, 0, 0, 0, 0, 1},
+			Err:   false,
+		},
+		{
+			Name:  "Field2",
+			Type:  gocql.TypeVarchar,
+			ValIn: []byte("test"),
+			Err:   false,
+		},
+		{
+			Name:  "InvalidField",
+			Type:  gocql.TypeBigInt,
+			ValIn: []byte("test"),
+			Err:   true,
+		},
+	}
+
+	// Create a UDTTestCase
+	testCase := testutils.UDTTestCase{
+		Obj:     udtInstance,
+		ObjName: "CustomUDT",
+		New:     func() gocql.UDTUnmarshaler { return &CustomUDT{} },
+		Fields:  udtFields,
+	}
+
+	testCase.Run(t)
+}