Add IsPrime tests

X10D.Tests/X10D.Tests.csproj

@@ -23,4 +23,9 @@
         <ProjectReference Include="..\X10D\X10D.csproj" />
     </ItemGroup>
 
+    <ItemGroup>
+        <None Remove="1000primes.txt" />
+        <EmbeddedResource Include="1000primes.txt" />
+    </ItemGroup>
+
 </Project>

X10D.Tests/src/Core/IsPrimeTests.cs

@@ -0,0 +1,121 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Text;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace X10D.Tests.Core
+{
+    /// <summary>
+    ///     Tests for <see cref="Int32Extensions.IsPrime(int)"/>.
+    /// </summary>
+    /// <remarks>
+    ///     Tests for this extension method are delegated to their own test class because of the non-trivial requirements for
+    ///     loading testing prime numbers.
+    /// </remarks>
+    /// <seealso cref="Int32Extensions.IsPrime(int)" />
+    [TestClass]
+    public class IsPrimeTests
+    {
+        private IReadOnlyList<int> _primeNumbers = ArraySegment<int>.Empty;
+
+        [TestInitialize]
+        public void Initialize()
+        {
+            _primeNumbers = LoadPrimes();
+            Assert.AreEqual(1000, _primeNumbers.Count);
+        }
+
+        /// <summary>
+        ///     Asserts the primality of the first 1000 known prime numbers. 
+        /// </summary>
+        [TestMethod]
+        public void First1000Primes()
+        {
+            for (var index = 0; index < _primeNumbers.Count; index++)
+            {
+                var value = _primeNumbers[index];
+                var result = value.IsPrime();
+                Assert.IsTrue(result, value.ToString("N0", CultureInfo.InvariantCulture));
+            }
+        }
+
+        /// <summary>
+        ///     Asserts that all negative numbers are not prime.
+        /// </summary>
+        [TestMethod]
+        public void Negatives()
+        {
+            for (var value = short.MinValue; value < 0; value++)
+            {
+                var result = value.IsPrime();
+                Assert.IsFalse(result, value.ToString("N0", CultureInfo.InvariantCulture));
+            }
+        }
+
+        /// <summary>
+        ///     Asserts that all negative numbers are not prime.
+        /// </summary>
+        [TestMethod]
+        public void LessThan2()
+        {
+            for (var value = 0; value < 2; value++)
+            {
+                var result = value.IsPrime();
+                Assert.IsFalse(result, value.ToString("N0", CultureInfo.InvariantCulture));
+            }
+        }
+
+        /// <summary>
+        ///     Tests the primality of the numbers 0 - 7919.
+        /// </summary>
+        [TestMethod]
+        public void ZeroTo7919()
+        {
+            for (var value = 0; value < 7920; value++)
+            {
+                var expected = _primeNumbers.Contains(value);
+                var actual = value.IsPrime();
+
+                Assert.AreEqual(expected, actual, value.ToString("N0", CultureInfo.InvariantCulture));
+            }
+        }
+
+        /// <summary>
+        ///     Tests the primality of the numbers 0 - <see cref="byte.MaxValue" />.
+        /// </summary>
+        [TestMethod]
+        public void ZeroToByteMaxValue()
+        {
+            for (byte value = 0; value < byte.MaxValue; value++)
+            {
+                var expected = _primeNumbers.Contains(value);
+                var actual = value.IsPrime();
+
+                Assert.AreEqual(expected, actual, value.ToString("N0", CultureInfo.InvariantCulture));
+            }
+        }
+
+        private static IReadOnlyList<int> LoadPrimes()
+        {
+            using var stream = Assembly.GetExecutingAssembly().GetManifestResourceStream("X10D.Tests.1000primes.txt");
+            Assert.IsNotNull(stream);
+
+            using var reader = new StreamReader(stream, Encoding.UTF8);
+            var primes = new List<int>();
+
+            while (reader.ReadLine() is { } line)
+            {
+                if (int.TryParse(line, out var prime))
+                {
+                    primes.Add(prime);
+                }
+            }
+
+            return primes.AsReadOnly();
+        }
+    }
+}