Problem z testowaniem Deleta w SpringBoot MockMvc

  @Test
    @DisplayName("Should delete Classes Box by Id ")
    void shouldDeleteClassBlockById() throws Exception {

        this.mockMvc
                .perform(delete("/classBlocks?classBlockId=1"))
                .andDo(print())
                .andExpect(status().isOk());

        /* TODO - why?whyyyyyyyyyyyyy???
            log:
            org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint ["FKvpqxtuay01bo3jtvv8uijs5c: PUBLIC.courses_class_block_list FOREIGN KEY(class_block_list_id) REFERENCES PUBLIC.class_block(id) (CAST(1 AS BIGINT))"; SQL statement:
            delete from class_block where id=? [23503-214]]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement
         */
    }

@DeleteMapping
    public ResponseEntity<HttpStatus> deleteClassBlock(@RequestParam("classBlockId") Long id) {
        return classBlockService.deleteClassBlock(id);
    }

public ResponseEntity<HttpStatus> deleteClassBlock(Long id) {
        ClassBlock classBlock = classBlockRepository
                .findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Class Block with id:" + id + "not exist"));

        classBlockRepository.delete(classBlock);
        return new  ResponseEntity<>(HttpStatus.NO_CONTENT);
    }

package com.example.trainingmanagementsystem.Model;

import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;

import javax.persistence.*;

import java.util.LinkedList;
import java.util.List;

@Entity
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class ClassBlock {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "CLASS_BLOCK_NAME")
    private String name;

    @OneToMany
    private List<Classes> classesList = new LinkedList<>();

}

@OneToMany(orphanRemoval = true, cascade = CascadeType.REMOVE)

@Entity
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class Classes {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "TOPIC")
    private String topic;

    @Column(name = "DATE")
    @DateTimeFormat(iso = DateTimeFormat.ISO.DATE, pattern = "yyyy-MM-dd")
    private LocalDate date;
}