[SPARK-13419][SQL] Update SubquerySuite to use checkAnswer for validation

[lresende]

What changes were proposed in this pull request?

Change SubquerySuite to validate test results utilizing checkAnswer helper method

How was this patch tested?

Existing tests

[SparkQA]

Test build #55416 has finished for PR 12269 at commit d0652c9.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #55691 has finished for PR 12269 at commit e58cf23.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[davies]

cc @liancheng , who knows more in SQL generation

[lresende]

@davies @liancheng
So, when converting these tests, I noticed that the following :
test("uncorrelated scalar subquery on a DataFrame generated query") {
val df = Seq((1, "one"), (2, "two"), (3, "three")).toDF("key", "value")
df.registerTempTable("subqueryData")

checkAnswer(
  sql("select (select key from subqueryData where key > 2 order by key limit 1) + 1"),
  Array(Row(4))
)

}

Will fail with different plans, e.g.:

Project [(subquery#9 + 1) AS (scalarsubquery() + 1)#11]
: +- SubqueryAlias subquery#9
: +- GlobalLimit 1
: +- LocalLimit 1
: +- Sort [key#5 ASC], true
: +- Project [key#5]
: +- Filter (key#5 > 2)
: +- SubqueryAlias subqueryData
: +- Project [_1#2 AS key#5,_2#3 AS value#6]
: +- LocalRelation [_1#2,_2#3], [[0,1,1800000003,656e6f],[0,2,1800000003,6f7774],[0,3,1800000005,6565726874]]
+- OneRowRelation$

Project [(subquery#9 + 1) AS (scalarsubquery() + 1)#11]
: +- SubqueryAlias subquery#9
: +- GlobalLimit 1
: +- LocalLimit 1
: +- Sort [key#5 ASC], true
: +- Project [key#5]
: +- Filter (key#5 > 2)
: +- SubqueryAlias subqueryData
: +- Project [_1#2 AS key#5,_2#3 AS value#6]
: +- LocalRelation [_1#2,_2#3], [null,null,null]
+- OneRowRelation$

During some debuging I was tracking it down to TreeNode.parseToJson, where the missing data is falling into the case _ and not being properly added to json... but the actual fix might be in a different place.

Any thoughts on this issue ?

[lresende]

@davies @liancheng looks like after re basing to latest code, this issue has been resolved. I am going to wait for a build to complete to double check.

[SparkQA]

Test build #56307 has finished for PR 12269 at commit 79b49b7.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[davies]

LGTM,
Merging this into master, thanks!