Asserting UUID in junit

Question

I have a method which builds an object and returns it.

The object as UUID as one of its fields. While building the object, random UUID is generated. Here is the code:

public MetaData getMetaData(String id) {
  return MetaData.newBuilder().setId(id)
    .setCorrelationId(UUID.randomUUID().toString())
    .setCreatedAt(now(UTC).format(ISO_ZONED_DATE_TIME))
    .build();
}

Here is my test:

@Test
public void shouldVerifyIfTheMetaDataIsBuild() {

  MetaData metaData = handler.getMetaData("1234");

  assertThat(metaData.getId(), is("1234"));
  assertThat(metaData.getCorrelationId(), isNotNull());
}

I'm just verifying if the correlationId is not null or not. Is there a better way to verify the UUID?

Answer 1

The only way to verify the current production code is to, yes, check that CorrelationId is not null. You could also check that the layout of the expected string matches a valid UUID string.

Of course, when you want to a bit of better checking, then you simply have to replace UUID.randomUUID().toString() with something that you can control.

For example you could create a UUIDGenerator interface, with a default method that creates a random UUID, as shown in your code. But in your test setup, you instead provide an implementation of that interface that returns a specific UUID.

Then your test code could know which UUID should be used, and assertThat(actualUuid, is(expectedUuid)).

Answer 2

I would change this line:

assertThat(metaData.getCorrelationId().toString(), isNotNull());

to the following:

assertThat(metaData.getCorrelationId(), isNotNull());

otherwise you would get a NullPointerException if metaData.getCorrelationId() returns null instead of an assertion failure.

Additionally, you could test if metaData.getCorrelationId() returns a string that represents a valid UUID, by trying to parse it:

try {
    UUID.fromString(metaData.getCorrelationID());
} catch (IllegalArgumentException e) {
    fail("Correlation ID is not a valid UUID: " + metaData.getCorrelationId());
}