[C++] Add tests for HalfFloatScalar

[pitrou]

Describe the enhancement requested

We have this long-standing TODO in scalar_test.cc that we should be able to address now that we have better float16 support in the library:

arrow/cpp/src/arrow/scalar_test.cc

Line 1174 in 85b4e6d

// TODO test HalfFloatScalar

Component(s)

C++

[pitrou]

@dinse I don't know if you're interested in this.

[dinse]

I added HalfFloatType to the params for TestRealScalar. Then, the equality comparisons fail for NaN and 0/-0, which I think is related to #46739.

[andishgar]

Describe the enhancement requested

We have this long-standing TODO in scalar_test.cc that we should be able to address now that we have better float16 support in the library:

arrow/cpp/src/arrow/scalar_test.cc

Line 1174 in 85b4e6d

// TODO test HalfFloatScalar

Component(s)

C++

@pitrou While working on this pull request, I realized that there are no such tests for Array, ChunkedArray, RecordBatch, or Table .

[benibus]

This is potentially handled in #46973 (along with the Array tests).