Add preliminary test and test framework changes for ExistanceJoin

[gerashegalov]

1. Allow matching short TreeNode string against a regex.
2. which enables us to ensure that the test exhibits ExistenceJoin

Contributes to #589

Signed-off-by: Gera Shegalov gera@apache.org

[gerashegalov]

build

[revans2]

The code looks fine. I am just a little confused why this needs to be split off from the rest of the ExistanceJoin code. I guess adding in the regular expression check is technically unrelated, but then I would prefer to see that as a separate PR without the xfail test.

If I saw "Add an xfail'd test for ExistenceJoin" in the changelog I would be confused and not know why we did that or what it was all about.

[gerashegalov]

The code looks fine. I am just a little confused why this needs to be split off from the rest of the ExistanceJoin code. I guess adding in the regular expression check is technically unrelated, but then I would prefer to see that as a separate PR without the xfail test.

It does not have to, but I thought I create it as a tiny milestone in the test-first approach. I can keep working on this branch until the feature is done and there is no need for xfail.

If I saw "Add an xfail'd test for ExistenceJoin" in the changelog I would be confused and not know why we did that or what it was all about.

I will make it more clear if we are going to keep the test-only PR

[gerashegalov]

build