Clarify error message when a job uses an input multiple times.

[psobot]

Given a Scio job that uses the same input multiple times:

object JobWithDuplicateInput {
  def main(cmdlineArgs: Array[String]): Unit = {
    val (sc, args) = ContextAndArgs(cmdlineArgs)
    sc.textFile(args("input"))
    sc.textFile(args("input"))
    sc.close()
  }
}

...Scio's TestDataManager currently throws an error in test that reads: There already exists test input for..., which implies that the test itself has multiples of the same test input. This is unclear as the issue is actually with the job itself, not the test.

This PR clarifies this error message by changing it to s"Test input $key has already been used once.", which is hopefully clearer for users that encounter this error.

(cc @clairemcginty, @regadas)

[codecov]

Codecov Report

Merging #1720 into master will decrease coverage by 2.58%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1720      +/-   ##
==========================================
- Coverage    71.6%   69.02%   -2.59%     
==========================================
  Files         175      175              
  Lines        5364     5359       -5     
  Branches      328      314      -14     
==========================================
- Hits         3841     3699     -142     
- Misses       1523     1660     +137

Impacted Files	Coverage Δ
...ala/com/spotify/scio/testing/TestDataManager.scala	100% <100%> (ø)	⬆️
.../spotify/scio/bigquery/client/BigQueryConfig.scala	0% <0%> (-83.34%)	⬇️
...scala/com/spotify/scio/bigquery/client/Cache.scala	0% <0%> (-66.67%)	⬇️
.../spotify/scio/bigquery/BigQueryPartitionUtil.scala	0% <0%> (-58.98%)	⬇️
...scala/com/spotify/scio/bigquery/BigQueryUtil.scala	50% <0%> (-50%)	⬇️
...la/com/spotify/scio/bigquery/client/QueryOps.scala	0.79% <0%> (-48.42%)	⬇️
...com/spotify/scio/bigquery/types/BigQueryType.scala	37.5% <0%> (-25%)	⬇️
...la/com/spotify/scio/bigquery/client/TableOps.scala	0% <0%> (-22.37%)	⬇️
...la/com/spotify/scio/bigquery/client/BigQuery.scala	27.02% <0%> (-10.82%)	⬇️
...n/scala/com/spotify/scio/bigquery/BigQueryIO.scala	24.29% <0%> (-3.74%)	⬇️
... and 2 more

---

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[clairemcginty]

awesome, thanks for the PR!

[clairemcginty]

🎨 "used once" -> "read once"?

while you're at it, would you want to make a matching change to TestOutput? :)

[psobot]

👍

[clairemcginty]

heh thanks for fixing the typos!

[psobot]

Changes made - thanks for the review, @clairemcginty!

[clairemcginty]

thanks for the contribution! looks great 👍