Test failures in a Kotlin spring project

Project: https://github.com/spring-guides/tut-spring-boot-kotlin.git

appmap.yml:

# appmap.yml
name: MyFirstKotlin/AppMap

packages:
  # List the packages you'd like to record here.
  - path: com.example.blog

agent.log

Shell output:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.2.2.RELEASE)

2021-03-23 16:55:21.332  WARN 76617 --- [           main] o.s.boot.StartupInfoLogger               : InetAddress.getLocalHost().getHostName() took 5006 milliseconds to respond. Please verify your network configuration (macOS machines may need to add entries to /etc/hosts).
2021-03-23 16:55:26.340  INFO 76617 --- [           main] com.example.blog.HttpControllersTests    : Starting HttpControllersTests on Ubehebe.local with PID 76617 (started by ptrdvrk in /Users/ptrdvrk/work/github/java/tut-spring-boot-kotlin)
2021-03-23 16:55:26.341  INFO 76617 --- [           main] com.example.blog.HttpControllersTests    : No active profile set, falling back to default profiles: default
2021-03-23 16:55:32.245  INFO 76617 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2021-03-23 16:55:32.373  INFO 76617 --- [           main] o.s.b.t.m.w.SpringBootMockServletContext : Initializing Spring TestDispatcherServlet ''
2021-03-23 16:55:32.373  INFO 76617 --- [           main] o.s.t.web.servlet.TestDispatcherServlet  : Initializing Servlet ''
2021-03-23 16:55:32.377  INFO 76617 --- [           main] o.s.t.web.servlet.TestDispatcherServlet  : Completed initialization in 4 ms
2021-03-23 16:55:32.393  INFO 76617 --- [           main] com.example.blog.HttpControllersTests    : Started HttpControllersTests in 21.094 seconds (JVM running for 72.569)
2021-03-23 16:55:32.829  WARN 76617 --- [           main] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: no answer found for: Iterable(child of com.example.blog.ArticleRepository#0 bean#2#3).iterator(); nested exception is com.fasterxml.jackson.databind.JsonMappingException: no answer found for: Iterable(child of com.example.blog.ArticleRepository#0 bean#2#3).iterator()]

MockHttpServletRequest:
      HTTP Method = GET
      Request URI = /api/article/
       Parameters = {}
          Headers = [Accept:"application/json"]
             Body = <no character encoding set>
    Session Attrs = {}

Handler:
             Type = com.example.blog.ArticleController
           Method = com.example.blog.ArticleController#findAll()

Async:
    Async started = false
     Async result = null

Resolved Exception:
             Type = org.springframework.http.converter.HttpMessageNotWritableException

ModelAndView:
        View name = null
             View = null
            Model = null

FlashMap:
       Attributes = null

MockHttpServletResponse:
           Status = 500
    Error message = null
          Headers = [Content-Type:"application/json"]
     Content type = application/json
             Body =
    Forwarded URL = null
   Redirected URL = null
          Cookies = []
2021-03-23 16:55:32.882  WARN 76617 --- [           main] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: no answer found for: Iterable(child of com.example.blog.UserRepository#0 bean#1#4).iterator(); nested exception is com.fasterxml.jackson.databind.JsonMappingException: no answer found for: Iterable(child of com.example.blog.UserRepository#0 bean#1#4).iterator()]

MockHttpServletRequest:
      HTTP Method = GET
      Request URI = /api/user/
       Parameters = {}
          Headers = [Accept:"application/json"]
             Body = <no character encoding set>
    Session Attrs = {}

Handler:
             Type = com.example.blog.UserController
           Method = com.example.blog.UserController#findAll()

Async:
    Async started = false
     Async result = null

Resolved Exception:
             Type = org.springframework.http.converter.HttpMessageNotWritableException

ModelAndView:
        View name = null
             View = null
            Model = null

FlashMap:
       Attributes = null

MockHttpServletResponse:
           Status = 500
    Error message = null
          Headers = [Content-Type:"application/json"]
     Content type = application/json
             Body =
    Forwarded URL = null
   Redirected URL = null
          Cookies = []
[ERROR] Tests run: 2, Failures: 2, Errors: 0, Skipped: 0, Time elapsed: 21.598 s <<< FAILURE! - in com.example.blog.HttpControllersTests
[ERROR] List articles  Time elapsed: 0.446 s  <<< FAILURE!
java.lang.AssertionError: Status expected:<200> but was:<500>
	at com.example.blog.HttpControllersTests.List articles(HttpControllersTests.kt:30)

[ERROR] List users  Time elapsed: 0.029 s  <<< FAILURE!
java.lang.AssertionError: Status expected:<200> but was:<500>
	at com.example.blog.HttpControllersTests.List users(HttpControllersTests.kt:44)

Start with the linked tut-spring-boot-kotlin project and run HttpControllersTests.kt, especially the assertions at lines 30 and 44. Review the attached agent.log alongside the failures for GET /api/article/ and GET /api/user/; done means both tests pass with the expected 200 status and no reported serialization error.