[SPARK-8652] [PYSPARK] Check return value for all uses of doctest.testmod()

This patch addresses a critical issue in the PySpark tests:

Several of our Python modules' `__main__` methods call `doctest.testmod()` in order to run doctests but forget to check and handle its return value. As a result, some PySpark test failures can go unnoticed because they will not fail the build.

Fortunately, there was only one test failure which was masked by this bug: a `pyspark.profiler` doctest was failing due to changes in RDD pipelining.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #7032 from JoshRosen/testmod-fix and squashes the following commits:

60dbdc0 [Josh Rosen] Account for int vs. long formatting change in Python 3
8b8d80a [Josh Rosen] Fix failing test.
e6423f9 [Josh Rosen] Check return code for all uses of doctest.testmod().

1 files changed, 3 insertions, 1 deletions

diff --git a/dev/merge_spark_pr.py b/dev/merge_spark_pr.py
index cd83b352c1..cf827ce89b 100755
--- a/dev/merge_spark_pr.py
+++ b/dev/merge_spark_pr.py
@@ -431,6 +431,8 @@ def main():
 
 if __name__ == "__main__":
     import doctest
-    doctest.testmod()
+    (failure_count, test_count) = doctest.testmod()
+    if failure_count:
+        exit(-1)
     
     main()