[BEAM-3112] Improve error messages in ElasticsearchIO test utils

[echauchot]

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R: @iemejia

[jbonofre]

R: @jbonofre

[iemejia]

retest this please

[iemejia]

LGTM, waiting for jenkins to merge.
If you think it is worth the effort maybe it is a good idea to add a test method for checkForErrors to validate its resiliance in case of missing fields.

[jbonofre]

Lgtm

[iemejia]

Minor minor comment, don't forget to add an extra space before curly braces (I will fix this on merge).
See point 3 on https://google.github.io/styleguide/javaguide.html#s4.6.2-horizontal-whitespace

[echauchot]

Thanks for the review guys!
@iemejia
1.checkForErrors is already tested in ElasticsearchIOTest.testWriteWithErrors which tries to insert 2 malformed docs. I just added a call to this method in ElasticsearchTestUtils.insertTestDocuments
2. about the curly braces, I thought about adding this rule to checktyle.xml

[echauchot]

retest this please

[iemejia]

@echauchot It is a good idea to fix the braces issue on the checkstyle if you find a way to enforce it (I am surprised it is not enforced there), from a quicklook however it seems you will need to fix ~70 classes that don't respect the braces style.