[repo-assist] test: add coverage-gap tests for Frac, Pow, Divide, and Clamp

tests/FixedPointNano.Tests/FixedPointNanoCoverageGapTests.cs

@@ -0,0 +1,84 @@
+using System;
+using Seerstone;
+
+namespace Seerstone.Tests;
+
+/// <summary>
+/// Covers behaviours not exercised by the other test fixtures:
+/// <c>Frac</c>, <c>Pow</c> negative-exponent guard, <c>Divide(long)</c> zero guard,
+/// and <c>Clamp</c> invalid-range guard.
+/// </summary>
+[TestFixture]
+public sealed class FixedPointNanoCoverageGapTests
+{
+    // -----------------------------------------------------------------------------------------
+    // Frac
+    // -----------------------------------------------------------------------------------------
+
+    [TestCase(1.75, 0.75, Description = "Positive fractional part")]
+    [TestCase(1.0, 0.0, Description = "Exact integer has zero Frac")]
+    [TestCase(-1.25, -0.25, Description = "Negative fractional part keeps sign")]
+    [TestCase(0.0, 0.0, Description = "Zero has zero Frac")]
+    public void FracShouldReturnFractionalPart(double input, double expected)
+    {
+        var value = FixedPointNano.FromDouble(input);
+        Assert.That(FixedPointNano.Frac(value).ToDouble(), Is.EqualTo(expected).Within(1e-9));
+    }
+
+    [Test]
+    public void FracShouldMatchFractionalPart()
+    {
+        var values = new[] { 1.5, -3.25, 0.0, 42.0, -0.999999999 };
+        foreach (var d in values)
+        {
+            var v = FixedPointNano.FromDouble(d);
+            Assert.That(FixedPointNano.Frac(v), Is.EqualTo(FixedPointNano.FractionalPart(v)),
+                $"Frac and FractionalPart differ for {d}");
+        }
+    }
+
+    // -----------------------------------------------------------------------------------------
+    // Pow – negative exponent guard
+    // -----------------------------------------------------------------------------------------
+
+    [Test]
+    public void PowShouldThrowForNegativeExponent()
+    {
+        Assert.That(
+            () => FixedPointNano.Pow(FixedPointNano.One, -1),
+            Throws.TypeOf<ArgumentOutOfRangeException>());
+    }
+
+    [Test]
+    public void PowZeroExponentShouldReturnOne()
+    {
+        var value = FixedPointNano.FromDecimal(7.5m);
+        Assert.That(FixedPointNano.Pow(value, 0), Is.EqualTo(FixedPointNano.One));
+    }
+
+    // -----------------------------------------------------------------------------------------
+    // Divide(FixedPointNano, long) – zero-divisor guard
+    // -----------------------------------------------------------------------------------------
+
+    [Test]
+    public void DivideByLongZeroShouldThrowDivideByZeroException()
+    {
+        Assert.That(
+            () => FixedPointNano.Divide(FixedPointNano.One, 0L),
+            Throws.TypeOf<DivideByZeroException>());
+    }
+
+    // -----------------------------------------------------------------------------------------
+    // Clamp – invalid range guard
+    // -----------------------------------------------------------------------------------------
+
+    [Test]
+    public void ClampShouldThrowWhenMinExceedsMax()
+    {
+        var min = FixedPointNano.FromDecimal(5m);
+        var max = FixedPointNano.FromDecimal(1m);
+        Assert.That(
+            () => FixedPointNano.Clamp(FixedPointNano.Zero, min, max),
+            Throws.TypeOf<ArgumentException>());
+    }
+}