JsonClassPathSource support generics type?

[sherlockEix]

Hello. I've tried the demo below but it doesn't work. I think JsonClassPathSource can't deserialize json array to java list. Is there any other way to implement it? Thanks.

Java code:

@JsonClassPathSource("test.json")
void test(List<Person> persons){
  log.info("{}",persons)
}

Json file:

[
  {
    "name": "a",
    "age": 23
  },
  {
    "name": "a",
    "age": 23
  }
]

[Michael1993]

Hi there @sherlockEix !

Just for the sake of completeness, could you also copy here your Person class and the exception message (I assume) you get when trying to execute the test above?

[sherlockEix]

yes. this is my demo. i hope that jedisList can be deserialized from JEDIS path

• java code

private static final String JEDIS = "org/junitpioneer/jupiter/json/jedis.json";
@ParameterizedTest
@JsonClasspathSource(JEDIS)
void listObject(List<Jedi> jedisList){
	System.out.println("jedisList = " + jedisList);
}

• jedis content

[
  {
    "name": "Luke",
    "height": 172
  },
  {
    "name": "Yoda",
    "height": 66
  }
]

• error

Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList<java.lang.Object>` from Object value (token `JsonToken.START_OBJECT`)
 at [Source: UNKNOWN; byte offset: #UNKNOWN]

[Michael1993]

Oh, yeah, I see where the problem is - you pass a list of objects to your test that expects a list of lists. See, when you execute a parameterized test, it expects an input (a list) which it converts to single parameters. In your example your parameter is a list, so the test tries to convert your input to a list but it can not do that because you supplied a simple list not a list of lists.

To demonstrate with an example, this should work:

@ParameterizedTest
@JsonClasspathSource(JEDI_LIST)
void listObject(List<Jedi> jedisList){
	System.out.println("jedisList = " + jedisList);
}

Jedi list:

[
  [
    {
      "name": "Luke",
      "height": 172
    },
    {
      "name": "Yoda",
      "height": 66
    }
  ]
]

Note that I used two square brackets [ ] in my JSON file - because I want to pass a list of lists.

[Michael1993]

This actually makes me wonder why you would want to use a List as an input parameter. Do you want to test something on a collection of objects at the same time? Carefully examine your test - if you use a for loop or any other method to iterate and/or examine single objects in your passed List you might want to reconsider letting the ParameterizedTest do the iteration for you and just writing a test with a single object in mind.

Again to demonstrate with an example, let's say you want to test a performance review system. This approach would be wrong:

@ParameterizedTest
@EmployeeTeamsSource
void employeeScoresShouldExceedMinimum(List<Employee> employees) {
  for (Employee employee : employees) {
    assertThat(employee.performanceScore()).isGreaterThan(SCORE_MIN);
  }
}

In the above example you are testing individual objects, but you pass them in a list, which makes your test less readable. The correct approach in this case would be:

@ParameterizedTest
@EmployeeSource
void employeeScoresShouldExceedMinimum(Employee employee) {
  assertThat(employee.performanceScore()).isGreaterThan(SCORE_MIN);
}

Which is basically the same test, except it lets the test unwrap your collection. This isn't always the right approach, of course. For example, you might want to evaluate the weighted average of performance scores in teams (a collection of employees). Then passing a List would be a correct approach because you need information from multiple individual objects in a single test.

@ParameterizedTest
@EmployeeTeamsSource
void employeeScoresShouldExceedMinimum(List<Employee> employees) {
  assertThat(calculateWeightedAverage(employees)).isGreaterThan(SCORE_MIN);
}

[sherlockEix]

i want use @JsonClasspathSource to prepare my integrate test data. i would like to write data to json file. it's a complex struct. maybe single object or list. then. i will use injected object(list) to do test. my first idea is i write a utils to load data and deserialize to object. but i found @JsonClasspathSource so i use it to prepare my complex test data.