test-gap backlog fixes

1-tests/Just.PreciseMath.Tests/DoubleDoubleNumberStylesTests.cs

@@ -1,4 +1,5 @@
 using System.Globalization;
+using System.Numerics;
 using Shouldly;
 using Xunit;
 
@@ -6,6 +7,54 @@ namespace Just.PreciseMath.Tests;
 
 public class DoubleDoubleNumberStylesTests
 {
+    [Theory]
+    [InlineData(" 9,007,199,254,740,993 ", NumberStyles.Number, 9007199254740992.0, 1.0)]
+    [InlineData("-1.000000000000000055511151231257827021181583404541015625", NumberStyles.Float, -1.0, -5.5511151231257827e-17)]
+    public void GenericStyledParsingRetainsExactResidual(string text, NumberStyles style, double high, double low)
+    {
+        // Exact integers 2^53 + 1 and dyadic -(1 + 2^-54), not rounded double parses.
+        AssertGenericStyledParsing<DoubleDouble>(text, style, high, low);
+    }
+
+    [Theory]
+    [InlineData("1,000", NumberStyles.Float)]
+    [InlineData("1e+", NumberStyles.Any)]
+    [InlineData("not-a-number", NumberStyles.Number)]
+    public void GenericStyledParsingRejectsInvalidInput(string text, NumberStyles style)
+    {
+        AssertGenericStyledParsingFailure<DoubleDouble>(text, style);
+    }
+
+    private static void AssertGenericStyledParsing<T>(string text, NumberStyles style, double high, double low)
+        where T : INumberBase<T>
+    {
+        T fromString = T.Parse(text, style, CultureInfo.InvariantCulture);
+        T fromSpan = T.Parse(text.AsSpan(), style, CultureInfo.InvariantCulture);
+        T.TryParse(text, style, CultureInfo.InvariantCulture, out T? triedString).ShouldBeTrue();
+        T.TryParse(text.AsSpan(), style, CultureInfo.InvariantCulture, out T? triedSpan).ShouldBeTrue();
+        foreach (T? parsed in new[] { fromString, fromSpan, triedString, triedSpan })
+        {
+            DoubleDouble value = parsed.ShouldBeOfType<DoubleDouble>();
+            value.High.ShouldBe(high);
+            value.Low.ShouldBe(low);
+        }
+    }
+
+    private static void AssertGenericStyledParsingFailure<T>(string text, NumberStyles style)
+        where T : INumberBase<T>
+    {
+        Should.Throw<FormatException>(() => T.Parse(text, style, CultureInfo.InvariantCulture));
+        Should.Throw<FormatException>(() => T.Parse(text.AsSpan(), style, CultureInfo.InvariantCulture));
+        T.TryParse(text, style, CultureInfo.InvariantCulture, out T? fromString).ShouldBeFalse();
+        T.TryParse(text.AsSpan(), style, CultureInfo.InvariantCulture, out T? fromSpan).ShouldBeFalse();
+        foreach (T? parsed in new[] { fromString, fromSpan })
+        {
+            DoubleDouble value = parsed.ShouldBeOfType<DoubleDouble>();
+            BitConverter.DoubleToInt64Bits(value.High).ShouldBe(0L);
+            BitConverter.DoubleToInt64Bits(value.Low).ShouldBe(0L);
+        }
+    }
+
     [Theory]
     [InlineData("123", NumberStyles.None, 123.0)]
     [InlineData("  -1.25e+2  ", NumberStyles.Float, -125.0)]