[SPARK-22890][TEST] Basic tests for DateTimeOperations

[wangyum]

What changes were proposed in this pull request?

Test Coverage for DateTimeOperations, this is a Sub-tasks for SPARK-22722.

How was this patch tested?

N/A

[SparkQA]

Test build #85330 has finished for PR 20061 at commit e8e4d11.

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

[SparkQA]

Test build #85418 has finished for PR 20061 at commit cfef0f1.

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

[gatorsmile]

LGTM

[gatorsmile]

Thanks! Merged to master.