Added base spec for testing Spark wrapping transformers

[tovbinm]

Related issues
Spark wrapping transformers were missing a test spec

Describe the proposed solution

1. Added SwTransformerSpec for testing Spark wrapping transformers
2. Factored out some common functionality between OpTransformerSpec and SwTransformerSpec into private TransformerSpecCommon
3. Updated OpIndexToStringTest to use it

[codecov]

Codecov Report

Merging #295 into master will decrease coverage by 0.17%.
The diff coverage is 51.11%.

@@            Coverage Diff             @@
##           master     #295      +/-   ##
==========================================
- Coverage   86.41%   86.23%   -0.18%     
==========================================
  Files         319      320       +1     
  Lines       10452    10471      +19     
  Branches      346      562     +216     
==========================================
- Hits         9032     9030       -2     
- Misses       1420     1441      +21

Impacted Files	Coverage Δ
...ala/com/salesforce/op/test/SwTransformerSpec.scala	0% <0%> (ø)
...ges/sparkwrappers/generic/SparkWrapperParams.scala	0% <0%> (ø)	⬆️
...ala/com/salesforce/op/test/OpTransformerSpec.scala	97.77% <100%> (ø)	⬆️
...cala/com/salesforce/op/cli/gen/ProblemSchema.scala	91.37% <0%> (-5.18%)	⬇️
...in/scala/com/salesforce/op/cli/gen/AvroField.scala	74.35% <0%> (-2.57%)	⬇️
...es/src/main/scala/com/salesforce/op/OpParams.scala	89.79% <0%> (+4.08%)	⬆️

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[wsuchy]

LGTM, I am just curious if checking the underlying type of the wrapper is really necessary.

[crupley]

aside from one typo, LGTM

[tovbinm]

LGTM, I am just curious if checking the underlying type of the wrapper is really necessary.

@wsuchy maybe not as it should be checked by compiler. But I dont think there is anything wrong to check in a test as well.

[salesforce-cla]

Thanks for the contribution! It looks like @tovbinm is an internal user so signing the CLA is not required. However, we need to confirm this.

[salesforce-cla]

Thanks for the contribution! Unfortunately we can't verify the commit author(s): Matthew Tovbin <m***@s***.com>. One possible solution is to add that email to your GitHub account. Alternatively you can change your commits to another email and force push the change. After getting your commits associated with your GitHub account, refresh the status of this Pull Request.