[SPARK-22990][Core] Fix method isFairScheduler in JobsTab and StagesTab

[gengliangwang]

What changes were proposed in this pull request?

In current implementation, the function isFairScheduler is always false, since it is comparing String with SchedulingMode

It works with this patch:

[cloud-fan]

good catch! LGTM

[SparkQA]

Test build #85801 has finished for PR 20186 at commit 10b5518.

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

[SparkQA]

Test build #85800 has finished for PR 20186 at commit fb87aa6.

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

[gengliangwang]

retest this please

[SparkQA]

Test build #85804 has finished for PR 20186 at commit 10b5518.

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

[vanzin]

Is it easy to add a unit test in StagePageSuite? Also this is the kind of stuff the compiler should be complaining about...

[cloud-fan]

I think it's fine. We usually don't test if a config can be correctly set as it's so trivial...

[cloud-fan]

thanks, merging to master/2.3!

[gengliangwang]

I just did a quick test with code changes, it works. Attach the screenshot in PR description.

[vanzin]

I think it's fine. We usually don't test if a config can be correctly set as it's so trivial...

The point is to test that the code using that config works as expected, not that it can be set. And as this PR proves, code can be wrong even in "trivial" cases.