ConnectionStub throws error when fetchAll is called on execute.

Yeah, by default the ConnectionStub always returns the array, that is wrong.
I fixed this by returning a mock of PDOStatement for select and integers for insert and delete actions.
See the MR.

Please test it and report if it works well for you.

Actually, to test your code, you should manually make a stub of the execute response, using this approach:

    $database = TestHelpers::service('database');
    $yourExpectedResult = [1, 2, 3];
    $executeMock = $this->createMock(\PDOStatement::class);
    $executeMock->method('fetchAll')->willReturn($yourExpectedResult);
    $database->stubSetExecuteHandler(function () use ($executeMock) {
      return $executeMock;
    }, 'select');
    $result = $database->select('table1')->execute()->fetchAll();
    $this->assertEquals($yourExpectedResult, $result);

I tested and merged this. If it will not help to you, please reopen the issue.

I'm no longer getting this error, I added some more detail in 📌 What is the proper way to inject the cache backend? Needs review with what I am experiencing now.