✨Add UnitsNetSetup to hold global static state (#1267)

Added `UnitsNetSetup` to gather global state in a single place as a
singleton, with the possibility of passing instances of it to static
methods later to override the defaults.

This way, state is no longer scattered among multiple classes that
depend on each other in non-obvious ways and where initialization order
has caused issues up until now.

### Changes
- Add `UnitsNetSetup` to hold global state as a singleton property
`Default` that controls default state initialization.
- Add properties for all "services" that depend on global state:
`UnitConverter, UnitAbbreviationsCache, UnitParser, QuantityParser`
- Forward all other `Default` singleton properties from these services
to `UnitsNetSetup.Default` and mark obsolete
- Add some TODOs where it seems functionality is missing

### Testing
❌ Still running into a handful of flaky tests due to racing conditions. 
This was a regression in #1210, but still not fixed.
Will investigate and fix in separate PR.

```
UnitAbbreviationsCacheTests.AllUnitsImplementToStringForInvariantCulture
UnitAbbreviationsCacheTests.MapUnitToAbbreviation_AddCustomUnit_DoesNotOverrideDefaultAbbreviationForAlreadyMappedUnits
```

UnitsNet.Serialization.JsonNet/AbbreviatedUnitsConverter.cs

@@ -45,7 +45,7 @@ public AbbreviatedUnitsConverter()
         /// </summary>
         /// <param name="comparer">The comparer used to compare the property/quantity names (e.g. StringComparer.OrdinalIgnoreCase) </param>
         public AbbreviatedUnitsConverter(IEqualityComparer<string?> comparer)
-            : this(new Dictionary<string, QuantityInfo>(Quantity.ByName, comparer), UnitAbbreviationsCache.Default, comparer)
+            : this(new Dictionary<string, QuantityInfo>(Quantity.ByName, comparer), UnitsNetSetup.Default.UnitAbbreviations, comparer)
         {
         }
 

UnitsNet.Tests/AlphabeticalOrderer.cs

@@ -0,0 +1,29 @@
+// Licensed under MIT No Attribution, see LICENSE file at the root.
+// Copyright 2013 Andreas Gullberg Larsen ([email protected]). Maintained at https://github.com/angularsen/UnitsNet.
+
+using System.Collections.Generic;
+using System.Linq;
+using Xunit.Abstractions;
+using Xunit.Sdk;
+
+namespace UnitsNet.Tests;
+
+/// <summary>
+///     Useful for debugging tests where a particular order of tests is required.
+/// </summary>
+/// <example>
+/// Add the attribute to your test class:
+/// <code>
+/// <![CDATA[
+/// [TestCaseOrderer(
+/// ordererTypeName: "UnitsNet.Tests.AlphabeticalOrderer",
+/// ordererAssemblyName: "UnitsNet.Tests")]
+/// ]]>
+/// </code>
+/// </example>
+public class AlphabeticalOrderer : ITestCaseOrderer
+{
+    public IEnumerable<TTestCase> OrderTestCases<TTestCase>(
+        IEnumerable<TTestCase> testCases) where TTestCase : ITestCase =>
+        testCases.OrderBy(testCase => testCase.TestMethod.Method.Name);
+}

UnitsNet.Tests/BaseUnitsTests.cs

@@ -140,13 +140,14 @@ public void ToStringGivesExpectedResult()
                 AmountOfSubstanceUnit.Mole,
                 LuminousIntensityUnit.Candela);
 
-            var m = UnitAbbreviationsCache.Default.GetDefaultAbbreviation(LengthUnit.Meter);
-            var kg = UnitAbbreviationsCache.Default.GetDefaultAbbreviation(MassUnit.Kilogram);
-            var s = UnitAbbreviationsCache.Default.GetDefaultAbbreviation(DurationUnit.Second);
-            var A = UnitAbbreviationsCache.Default.GetDefaultAbbreviation(ElectricCurrentUnit.Ampere);
-            var K = UnitAbbreviationsCache.Default.GetDefaultAbbreviation(TemperatureUnit.Kelvin);
-            var mol = UnitAbbreviationsCache.Default.GetDefaultAbbreviation(AmountOfSubstanceUnit.Mole);
-            var cd = UnitAbbreviationsCache.Default.GetDefaultAbbreviation(LuminousIntensityUnit.Candela);
+            UnitAbbreviationsCache cache = UnitsNetSetup.Default.UnitAbbreviations;
+            var m = cache.GetDefaultAbbreviation(LengthUnit.Meter);
+            var kg = cache.GetDefaultAbbreviation(MassUnit.Kilogram);
+            var s = cache.GetDefaultAbbreviation(DurationUnit.Second);
+            var A = cache.GetDefaultAbbreviation(ElectricCurrentUnit.Ampere);
+            var K = cache.GetDefaultAbbreviation(TemperatureUnit.Kelvin);
+            var mol = cache.GetDefaultAbbreviation(AmountOfSubstanceUnit.Mole);
+            var cd = cache.GetDefaultAbbreviation(LuminousIntensityUnit.Candela);
 
             Assert.Equal($"[Length]: {m}, [Mass]: {kg}, [Time]: {s}, [Current]: {A}, [Temperature]: {K}, [Amount]: {mol}, [LuminousIntensity]: {cd}", siBaseUnits.ToString());
         }

UnitsNet.Tests/QuantityIFormattableTests.cs

@@ -27,11 +27,12 @@ public void EmptyOrNullFormatStringEqualsGFormat()
         [Fact]
         public void AFormatGetsAbbreviations()
         {
-            Assert.Equal(UnitAbbreviationsCache.Default.GetDefaultAbbreviation(MyLength.Unit, CultureInfo.InvariantCulture), MyLength.ToString("a", CultureInfo.InvariantCulture));
-            Assert.Equal(UnitAbbreviationsCache.Default.GetDefaultAbbreviation(MyLength.Unit, CultureInfo.InvariantCulture), MyLength.ToString("a0", CultureInfo.InvariantCulture));
+            UnitAbbreviationsCache cache = UnitsNetSetup.Default.UnitAbbreviations;
+            Assert.Equal(cache.GetDefaultAbbreviation(MyLength.Unit, CultureInfo.InvariantCulture), MyLength.ToString("a", CultureInfo.InvariantCulture));
+            Assert.Equal(cache.GetDefaultAbbreviation(MyLength.Unit, CultureInfo.InvariantCulture), MyLength.ToString("a0", CultureInfo.InvariantCulture));
 
-            Assert.Equal(UnitAbbreviationsCache.Default.GetUnitAbbreviations(MyLength.Unit, CultureInfo.InvariantCulture)[1], MyLength.ToString("a1", CultureInfo.InvariantCulture));
-            Assert.Equal(UnitAbbreviationsCache.Default.GetUnitAbbreviations(MyLength.Unit, CultureInfo.InvariantCulture)[2], MyLength.ToString("a2", CultureInfo.InvariantCulture));
+            Assert.Equal(cache.GetUnitAbbreviations(MyLength.Unit, CultureInfo.InvariantCulture)[1], MyLength.ToString("a1", CultureInfo.InvariantCulture));
+            Assert.Equal(cache.GetUnitAbbreviations(MyLength.Unit, CultureInfo.InvariantCulture)[2], MyLength.ToString("a2", CultureInfo.InvariantCulture));
         }
 
         [Fact]

UnitsNet.Tests/UnitAbbreviationsCacheTests.cs

@@ -229,6 +229,24 @@ public void GetDefaultAbbreviationFallsBackToUsEnglishCulture()
             Assert.Equal("US english abbreviation for Unit1", abbreviation);
         }
 
+        [Fact]
+        public void MapUnitToAbbreviation_DoesNotAffectOtherCacheInstances()
+        {
+            var culture = AmericanCulture;
+            var unit = AreaUnit.SquareMeter;
+
+            var cache1 = new UnitAbbreviationsCache();
+            cache1.MapUnitToAbbreviation(unit, culture, "m^2");
+
+            var cache2 = new UnitAbbreviationsCache();
+            cache2.MapUnitToAbbreviation(unit, culture, "m2");
+
+            Assert.Equal(new[] { "m²", "m^2" }, cache1.GetUnitAbbreviations(unit, culture));
+            Assert.Equal(new[] { "m²", "m2" }, cache2.GetUnitAbbreviations(unit, culture));
+            Assert.Equal("m²", cache1.GetDefaultAbbreviation(unit, culture));
+            Assert.Equal("m²", cache2.GetDefaultAbbreviation(unit, culture));
+        }
+
         [Fact]
         public void MapUnitToAbbreviation_AddCustomUnit_DoesNotOverrideDefaultAbbreviationForAlreadyMappedUnits()
         {

UnitsNet/CustomCode/Quantity.cs

@@ -9,15 +9,7 @@ namespace UnitsNet
 {
     public partial class Quantity
     {
-        static Quantity()
-        {
-            Default = new QuantityInfoLookup();
-        }
-
-        private static QuantityInfoLookup Default
-        {
-            get;
-        }
+        private static QuantityInfoLookup Default => UnitsNetSetup.Default.QuantityInfoLookup;
 
         /// <summary>
         /// All enum value names of <see cref="Infos"/>, such as "Length" and "Mass".

UnitsNet/CustomCode/QuantityParser.cs

@@ -37,7 +37,8 @@ public class QuantityParser
         /// <summary>
         ///     The default instance of <see cref="QuantityParser"/>, which uses <see cref="UnitAbbreviationsCache.Default"/> unit abbreviations.
         /// </summary>
-        public static QuantityParser Default { get; }
+        [Obsolete("Use UnitsNetSetup.Default.QuantityParser instead.")]
+        public static QuantityParser Default => UnitsNetSetup.Default.QuantityParser;
 
         /// <summary>
         ///     Creates an instance of <see cref="QuantityParser"/>, optionally specifying an <see cref="UnitAbbreviationsCache"/>
@@ -50,11 +51,6 @@ public QuantityParser(UnitAbbreviationsCache? unitAbbreviationsCache = null)
             _unitParser = new UnitParser(_unitAbbreviationsCache);
         }
 
-        static QuantityParser()
-        {
-            Default = new QuantityParser(UnitAbbreviationsCache.Default);
-        }
-
         /// <summary>
         ///     Parses a quantity from a string, such as "1.2 kg" to <see cref="Length"/> or "100 cm" to <see cref="Mass"/>.
         /// </summary>