Mocking a class instance affects the static instance initialization

[k-rus]

I have an unusual case with using Mockito and run into an interesting issue, which might be a feature of Java and Mockito or bug, but I wasn't able to figure it out. If it is not a bug, it would be great if you can answer and explain in my SO question.

I have a class with static instance of it and then I create a mock instance in my test, which results that the static instance is not initialized properly. Here relevant parts of the class definition code:

...
public class Schema implements SchemaProvider
{
    public static final Schema instance = new Schema();

    private volatile Keyspaces distributedKeyspaces = Keyspaces.none();

    private final Keyspaces localKeyspaces;

    private final boolean online;

    ...

    private Schema()
    {

        this.online = isDaemonInitialized();
        this.localKeyspaces = (FORCE_LOAD_LOCAL_KEYSPACES || isDaemonInitialized() || isToolInitialized())
                              ? Keyspaces.of(SchemaKeyspace.metadata(), SystemKeyspace.metadata())
                              : Keyspaces.none();
    }

    @VisibleForTesting
    public Schema(boolean online, Keyspaces localKeyspaces)
    {
        this.online = online;
        this.localKeyspaces = localKeyspaces;
    }
    ...

Then the project jar is used in another project where Schema is mocked in a test (Schema is not used before this):

Schema schema = Mockito.mock(Schema.class);

To my understanding this should not affect the static instance initialization, i.e., Schema.instance. However, I run into an issue that the static instance is not initialized correctly and its properties are null, i.e.:

assert Schema.instance.distributedKeyspaces == null;
assert Schema.instance.localKeyspaces == null;

I've found that I can workaround the initialization issue in my test project by loading it explicitly:

Class.forName(Schema.class.getName());
Schema schema = Mockito.mock(Schema.class);
// which gives me:
assert Schema.instance.distributedKeyspaces != null;
assert Schema.instance.localKeyspaces != null;

Java version: openjdk version "11.0.12" 2021-07-20

Mockito version: 3.5.0

[Delfic]

This is interesting as I have the opposite issue
Using Mockito.mockStatic(Schema.class) will initialize the class, which I don't want since I want to be able to mock static methods before