When to use classes

Hello Guys,

I have been an IBMi RPG programmer for around 10 years and finally getting a chance to write some java production level stuff.

I can figure out what a code is doing by looking at it and chatgpt is always there to help. But feeling confused when writing new stuff.

For ex, please see the below class:

class CompareResponsesTest {    @ParameterizedTest(name = "{index} - {0}")    @MethodSource("provideTestData")    void apiTest(String displayName, String s) throws Exception {        String response = IAC9360Client.sentRequestFromFile("IAC9360/request-" + s + ".xml");        assertThat(Input.fromString(response), isSimilarTo(Input.fromFile("IAC9SS0/result-" + s + ".xml")).withNodeFilter(node -> !node.getNodeName().equals("MICROSECS")).throwComparisonFailure());    }    private static Stream<Arguments> provideTestData() {        return Stream.of(                Arguments.of("ARTQA079 RULES PUBLDTE=19880708       C", "57852201"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA2=A C", "57852202"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA2=B C", "57852203"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA2=C C", "57852204"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA2=D C", "57852205"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA2=E C", "57852206"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA3=T C", "57852207"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA3=U C", "57852208"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA3=V C", "57852209"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA3=X C", "57852210"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA3=Y C", "57852211"),                Arguments.of("ARTQA079 RULES PUBLDTE=19880708 LA3=Z C", "57852212")        );    } }

This is a class which executes a junit test for a bunch of hardcoded values. I want to replace the hardcoded values to be dynamic by reading from an excel file. I figured out how to do this, but the question is should I use a new class for this example, TestData with a provideTestData method and modify the annotation as @MethodSource("TestData.provideTestData") OR could I just write it in the same method?

I am often having difficulties designing such stuff as RPG is mostly about modularising logic based on functionality which is straight forward to me. However in java in cases like this, not really sure if I should could just write a new method for this or an entirely new class. I guess what I am lacking is OOAD knowledge.

When do you use classes? Very simply, all the time.
That looks more like a JUnit question so I shall move you to a more appropriate forum.