DemoController.kt

package com.example.demo

import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.PathVariable
import org.springframework.web.bind.annotation.RestController
import java.util.*

@RestController
class DemoController {

    @GetMapping("test-uuid/{id}")
    fun getByUUID(@PathVariable id: UUID) {

    }
}

DemoControllerTest.kt

package com.example.demo

import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.test.web.servlet.MockMvc
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get
import org.springframework.test.web.servlet.result.MockMvcResultMatchers.status
import java.util.*


@SpringBootTest
@AutoConfigureMockMvc
class DemoControllerTest(@Autowired val mockMvc: MockMvc) {

    //success it is a 200
    @Test
    fun `testGetByUUID randomUUID`() {
        val id: UUID = UUID.randomUUID()
        mockMvc.perform(get("/test-uuid/$id"))
            .andExpect(status().isOk())
    }

    //success it is a 400
    @Test
    fun `testGetByUUID integer`() {
        mockMvc.perform(get("/test-uuid/1"))
            .andExpect(status().is4xxClientError())
    }

    //success it is a 400
    @Test
    fun `testGetByUUID u002f`() {
        mockMvc.perform(get("/test-uuid/\u002F"))
            .andExpect(status().is4xxClientError())
    }

    //fails with 500 error(MissingPathVariableException). Should be a 400
    @Test
    fun `testGetByUUID u001F`() {
        mockMvc.perform(get("/test-uuid/\u001F"))
            .andExpect(status().is4xxClientError())
    }

    //fails with 500 error(MissingPathVariableException). Should be again a 400
    @Test
    fun `testGetByUUID 000D`() {
        mockMvc.perform(get("/test-uuid/\u000D"))
            .andExpect(status().is4xxClientError())
    }
}

I'm curious why \u002F would behavior differently to \u001F, could you explain? @ltsallas