## What changes were proposed in this pull request?
This patch introduces SQLQueryTestSuite, a basic framework for end-to-end SQL test cases defined in spark/sql/core/src/test/resources/sql-tests. This is a more standard way to test SQL queries end-to-end in different open source database systems, because it is more manageable to work with files.
This is inspired by HiveCompatibilitySuite, but simplified for general Spark SQL tests. Once this is merged, I can work towards porting SQLQuerySuite over, and eventually also move the existing HiveCompatibilitySuite to use this framework.
Unlike HiveCompatibilitySuite, SQLQueryTestSuite compares both the output schema and the output data (in string form).
When there is a mismatch, the error message looks like the following:
```
[info] - blacklist.sql !!! IGNORED !!!
[info] - number-format.sql *** FAILED *** (2 seconds, 405 milliseconds)
[info] Expected "...147483648 -214748364[8]", but got "...147483648 -214748364[9]" Result should match for query #1 (SQLQueryTestSuite.scala:171)
[info] org.scalatest.exceptions.TestFailedException:
[info] at org.scalatest.Assertions$class.newAssertionFailedException(Assertions.scala:495)
[info] at org.scalatest.FunSuite.newAssertionFailedException(FunSuite.scala:1555)
[info] at org.scalatest.Assertions$class.assertResult(Assertions.scala:1171)
```
## How was this patch tested?
This is a test infrastructure change.
Author: petermaxlee <petermaxlee@gmail.com>
Closes#14472 from petermaxlee/SPARK-16866.
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