mkuthan opened a new issue, #28612:
URL: https://github.com/apache/beam/issues/28612
### What would you like to happen?
If element doesn't exist in empty PCollection - PAssert.thatSingleton emits
the following error message:
```
java.util.NoSuchElementException
org.apache.beam.sdk.Pipeline$PipelineExecutionException:
java.util.NoSuchElementException
(stack trace)
Caused by: java.util.NoSuchElementException
at java.base/java.util.ArrayList$Itr.next(ArrayList.java:970)
at
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterators.getOnlyElement(Iterators.java:309)
at
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterables.getOnlyElement(Iterables.java:263)
at
org.apache.beam.sdk.testing.PAssert$SingletonCheckerDoFn.processElement(PAssert.java:1613)
```
If element is not the only element in PCollection - PAssert.thatSingleton
emits the following error message:
```
java.lang.IllegalArgumentException: expected one element but was: (...)
org.apache.beam.sdk.Pipeline$PipelineExecutionException:
java.lang.IllegalArgumentException: expected one element but was: (...)
(stack trace)
Caused by: java.lang.IllegalArgumentException: expected one element but was:
(...) at
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterators.getOnlyElement(Iterators.java:323)
at
org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterables.getOnlyElement(Iterables.java:263)
at
org.apache.beam.sdk.testing.PAssert$SingletonCheckerDoFn.processElement(PAssert.java:1613)
```
For presented scenarios assertion errors doesn't really help - there is no
assertion call site info.
```
private static class SingletonCheckerDoFn ... {
@ProcessElement
public void processElement(ProcessContext c) {
ActualT actualContents = Iterables.getOnlyElement(c.element()); // <-
runtime exception here
c.output(doChecks(site, actualContents, checkerFn)); // <- no doCheck
call with proper assertion site info
}
}
```
### Issue Priority
Priority: 3 (nice-to-have improvement)
### Issue Components
- [ ] Component: Python SDK
- [X] Component: Java SDK
- [ ] Component: Go SDK
- [ ] Component: Typescript SDK
- [ ] Component: IO connector
- [ ] Component: Beam examples
- [ ] Component: Beam playground
- [ ] Component: Beam katas
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- [ ] Component: Flink Runner
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