Understanding why converting using aliases fails

[keitheweber]

Discussed in #789

^{Originally posted by keitheweber August 16, 2021}
I wrote a simple set of unit tests that would test converting from one unit to another when instantiating the unit objects by parsing a string. I am not sure what I am doing wrong, but most of these fail. It appears that the alias names defined in https://www.unidata.ucar.edu/software/udunits/udunits-2.2.28/udunits2-common.xml are not being honored?

Here's the source code for the unit tests

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.DynamicTest;
import org.junit.jupiter.api.TestFactory;
import ucar.units.Converter;
import ucar.units.Unit;
import ucar.units.UnitFormatManager;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

class ConversionTest {

    @TestFactory
    Stream<DynamicTest> conversionTests() {
        String[] unitNames = new String[]{
                "degK",
                "K",
                "deg_K",
                "degsK",
                "F",
                "deg_F",
                "degF",
                "C",
                "degC",
                "deg_C"
        };

        List<Unit> units = Arrays.stream(unitNames)
                .map(this::parse)
                .collect(Collectors.toList());

        return IntStream.range(0, units.size())
                .mapToObj(fromIndex -> IntStream.range(0, units.size())
                        .mapToObj(toIndex ->
                                DynamicTest.dynamicTest(unitNames[fromIndex] + " to " + unitNames[toIndex],
                                        () -> Assertions.assertDoesNotThrow(() -> convertTest(units.get(fromIndex), units.get(toIndex), 10.0)))
                        ).collect(Collectors.toList()))
                .flatMap(List::stream);
    }

    private double convertTest(Unit from, Unit to, double value) {
        try {
            if (!from.isCompatible(to)) {
                throw new RuntimeException("Units not compatible");
            }
            Converter converter = from.getConverterTo(to);
            return converter.convert(value);
        } catch (Exception ex) {
            throw new RuntimeException("Failed to convert", ex);
        }
    }

    private Unit parse(String name) {
        try {
            return UnitFormatManager.instance().parse(name);
        } catch (Exception e) {
            throw new RuntimeException("Failed to parse", e);
        }
    }
}
```</div>

[lesserwhirls]

Rather than keeping these in sync by hand, we'll need to refactor to pull definitions, aliases, etc. from the udunits-2 xml files. But, for now, the temperature aliases are in sync.