How can I ignore some JSON and object properties during unit testing?

I have a method that is migrating old JSON structure to a new one that I would like to test, but there is one randomly generated property (UUID) that I would like to ignore.

The interesting part of the object looks like this:

val expected = FooterContainer(id = UUID.fromString("11914145-9775-4675-9c65-54bbd369fb2c"), title = null, flowType=ContainerType.ROWS, elements=listOf() //the rest is not important.

The JSON to be converted looks totally different from this object, but this is the purpose of the method - to convert it to a new model.

val json = """[{"type": "list", "items": [{"link": "www.something.com", "type": "link", "label": "Some label"},
			{"type": "text", "label": "Another label"}, {"type": "text", "label": "Other label"},
			{"type": "text", "label": "yet another label"}, {"type": "text", "label": "info@something.com"}]

et cetera.

The below code worked as expected:

val gson: JsonElement = Gson().fromJson(json, JsonElement::class.java)

	// when
	val converted = with(ClientDataRepository()) {
		gson.readFooter()
	}

until I had to introduce a new field in FooterContainer object, which was val id: UUID

The method readFooter() is generating the UUID randomly, which is an expected behaviour.

But now, I cannot just assign a random (or hardcoded, as in the example code above) UUID to the expected class, which is logical - two randomly generated UUIDs will never be the same.

when I run the test, I obviously get:

Expected :FooterContainer(id=11914145-9775-4675-9c65-54bbd369fb2c,
Actual   :FooterContainer(id=7ba39ad0-1412-4fda-a827-0241916f8558,

Now, is there a possibility to ignore the id field for this test? It is not important from the test perspective, but the rest is.

You can simply copy the id field from the actual object to the expected:

val converted = with(ClientDataRepository()) {
    gson.readFooter()
}

val expected = FooterContainer(id = converted.id, title = null, flowType=ContainerType.ROWS, elements=listOf()) //the rest is not important.
Assertions.assertThat(converted).isEqualTo(expected);

If you are using assertJ, there is a stright forward solution:

Assertions.assertThat(converted).isEqualToIgnoringGivenFields(expected, "id")

Try JsonUnit. In this case you can modify your code in next way:

assertThatJson("{\"id\":${json-unit.ignore}}").isEqualTo("{\"id\": 11914145-9775-4675-9c65-54bbd369fb2c}");

You can use something like json-assert (https://github.com/skyscreamer/JSONassert) that support ignoring keys - https://stackoverflow.com/a/44328139/4473822