diff --git a/X10D.Tests/X10D.Tests.csproj b/X10D.Tests/X10D.Tests.csproj
new file mode 100644
index 0000000..41dc0ed
--- /dev/null
+++ b/X10D.Tests/X10D.Tests.csproj
@@ -0,0 +1,27 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>netcoreapp3.1</TargetFramework>
+        <IsPackable>false</IsPackable>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="Microsoft.CodeAnalysis.FxCopAnalyzers" Version="2.9.8">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.2.0" />
+        <PackageReference Include="MSTest.TestAdapter" Version="2.0.0" />
+        <PackageReference Include="MSTest.TestFramework" Version="2.0.0" />
+        <PackageReference Include="coverlet.collector" Version="1.0.1" />
+        <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.164">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\X10D\X10D.csproj" />
+    </ItemGroup>
+
+</Project>
\ No newline at end of file
diff --git a/X10D.Tests/src/BooleanTests.cs b/X10D.Tests/src/BooleanTests.cs
new file mode 100644
index 0000000..d9c8c26
--- /dev/null
+++ b/X10D.Tests/src/BooleanTests.cs
@@ -0,0 +1,26 @@
+namespace X10D.Tests
+{
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="BooleanExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class BooleanTests
+    {
+        /// <summary>
+        /// Tests for <see cref="BooleanExtensions.ToInt32"/>.
+        /// </summary>
+        [TestMethod]
+        public void ToInt32()
+        {
+            const bool a = true;
+            const bool b = false;
+
+            Assert.IsTrue(a);
+            Assert.IsFalse(b);
+            Assert.AreEqual(1, a.ToInt32());
+            Assert.AreEqual(0, b.ToInt32());
+        }
+    }
+}
diff --git a/X10D.Tests/src/ByteTests.cs b/X10D.Tests/src/ByteTests.cs
new file mode 100644
index 0000000..6ebed35
--- /dev/null
+++ b/X10D.Tests/src/ByteTests.cs
@@ -0,0 +1,103 @@
+namespace X10D.Tests
+{
+    using System.Collections.Generic;
+    using System.Text;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="ByteExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class ByteTests
+    {
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.AsString"/>.
+        /// </summary>
+        [TestMethod]
+        public void AsString()
+        {
+            byte[] a = { 0x00, 0x73, 0xc6, 0xff };
+            Assert.AreEqual("00-73-C6-FF", a.AsString());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.GetInt16"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetInt16()
+        {
+            byte[] a = { 0xF3, 0x3F };
+            Assert.AreEqual(16371, a.GetInt16());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.GetInt32"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetInt32()
+        {
+            byte[] a = { 0xB0, 0x0B, 0x13, 0x5F };
+            Assert.AreEqual(1595083696, a.GetInt32());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.GetInt64"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetInt64()
+        {
+            byte[] a = { 0xB0, 0x0B, 0x13, 0x50, 0x05, 0x31, 0xB0, 0x0B };
+            Assert.AreEqual(842227029206305712L, a.GetInt64());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.GetString(IEnumerable{byte})"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetString()
+        {
+            byte[] a = { 0x48, 0xc3, 0xa9, 0x6c, 0x6c, 0x6f, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64 };
+            Assert.AreEqual("Héllo World", a.GetString());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.GetString(IEnumerable{byte}, Encoding)"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetStringAscii()
+        {
+            byte[] a = { 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64 };
+            Assert.AreEqual("Hello World", a.GetString(Encoding.ASCII));
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.GetUInt16"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetUInt16()
+        {
+            byte[] a = { 0xF3, 0x3F };
+            Assert.AreEqual(16371, a.GetUInt16());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.GetUInt32"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetUInt32()
+        {
+            byte[] a = { 0xB0, 0x0B, 0x13, 0x5F };
+            Assert.AreEqual(1595083696U, a.GetUInt32());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ByteExtensions.GetUInt64"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetUInt64()
+        {
+            byte[] a = { 0xB0, 0x0B, 0x13, 0x50, 0x05, 0x31, 0xB0, 0x0B };
+            Assert.AreEqual(842227029206305712UL, a.GetUInt64());
+        }
+    }
+}
diff --git a/X10D.Tests/src/CharTests.cs b/X10D.Tests/src/CharTests.cs
new file mode 100644
index 0000000..c0f328d
--- /dev/null
+++ b/X10D.Tests/src/CharTests.cs
@@ -0,0 +1,35 @@
+namespace X10D.Tests
+{
+    using System;
+    using System.Linq;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="CharExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class CharTests
+    {
+        /// <summary>
+        /// Tests for <see cref="CharExtensions.Repeat"/>.
+        /// </summary>
+        [TestMethod]
+        public void Random()
+        {
+            var set = "abcdefghijklmnopqrstuvwxyz".ToCharArray();
+            var random = set.Random(20);
+
+            Assert.IsTrue(random.All(c => Array.IndexOf(set, c) >= 0));
+            Assert.IsFalse(random.Any(c => Array.IndexOf(set, c) < -1));
+        }
+
+        /// <summary>
+        /// Tests for <see cref="CharExtensions.Repeat"/>.
+        /// </summary>
+        [TestMethod]
+        public void Repeat()
+        {
+            Assert.AreEqual("aaaaaaaaaa", 'a'.Repeat(10));
+        }
+    }
+}
diff --git a/X10D.Tests/src/ComparableTests.cs b/X10D.Tests/src/ComparableTests.cs
new file mode 100644
index 0000000..7d27db9
--- /dev/null
+++ b/X10D.Tests/src/ComparableTests.cs
@@ -0,0 +1,22 @@
+namespace X10D.Tests
+{
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="ComparableExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class ComparableTests
+    {
+        /// <summary>
+        /// Tests for <see cref="ComparableExtensions.Between{T}"/>.
+        /// </summary>
+        [TestMethod]
+        public void Between()
+        {
+            Assert.IsTrue(5.Between(2, 7));
+            Assert.IsTrue(10.Between(9, 11));
+            Assert.IsFalse(100.Between(80, 99));
+        }
+    }
+}
diff --git a/X10D.Tests/src/ConvertibleTests.cs b/X10D.Tests/src/ConvertibleTests.cs
new file mode 100644
index 0000000..c366aea
--- /dev/null
+++ b/X10D.Tests/src/ConvertibleTests.cs
@@ -0,0 +1,58 @@
+namespace X10D.Tests
+{
+    using System;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="ConvertibleExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class ConvertibleTests
+    {
+        /// <summary>
+        /// Tests for <see cref="ConvertibleExtensions.To{T}"/>.
+        /// </summary>
+        [TestMethod]
+        public void To()
+        {
+            Assert.AreEqual(2, "2".To<int>());
+            Assert.AreEqual("12.5", 12.50.To<string>());
+            Assert.IsTrue("True".To<bool>());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ConvertibleExtensions.ToOrDefault{T}(System.IConvertible, System.IFormatProvider)"/>.
+        /// </summary>
+        [TestMethod]
+        public void ToOrDefault()
+        {
+            Assert.AreEqual(2, "2".ToOrDefault<int>());
+            Assert.AreEqual("12.5", 12.50.ToOrDefault<string>());
+            Assert.IsTrue("True".ToOrDefault<bool>());
+            Assert.ThrowsException<FormatException>(() => "Foo".ToOrDefault<double>());
+            Assert.IsTrue("1.5".ToOrDefault(out float f));
+            Assert.AreEqual(1.5f, f);
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ConvertibleExtensions.ToOrOther{T}(System.IConvertible, T, System.IFormatProvider)"/>.
+        /// </summary>
+        [TestMethod]
+        public void ToOrOther()
+        {
+            Assert.AreEqual(2.0, "Foo".ToOrOther(2.0));
+            Assert.IsFalse("Foo".ToOrOther(out var d, 2.0));
+            Assert.AreEqual(2.0, d);
+        }
+
+        /// <summary>
+        /// Tests for <see cref="ConvertibleExtensions.ToOrNull{T}(System.IConvertible, System.IFormatProvider)"/>.
+        /// </summary>
+        [TestMethod]
+        public void ToOrNull()
+        {
+            Assert.IsFalse("foo".ToOrNull(out ConvertibleTests t));
+            Assert.IsNull(t);
+        }
+    }
+}
diff --git a/X10D.Tests/src/DateTimeTests.cs b/X10D.Tests/src/DateTimeTests.cs
new file mode 100644
index 0000000..c7b6502
--- /dev/null
+++ b/X10D.Tests/src/DateTimeTests.cs
@@ -0,0 +1,107 @@
+namespace X10D.Tests
+{
+    using System;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="DateTimeExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class DateTimeTests
+    {
+        /// <summary>
+        /// Tests for <see cref="DateTimeExtensions.Age(DateTime)"/>.
+        /// </summary>
+        [TestMethod]
+        public void Age()
+        {
+            // no choice but to create dynamic based on today's date.
+            // age varies with time
+            DateTime now = DateTime.Now;
+            var dt = new DateTime(now.Year - 18, 1, 1);
+
+            Assert.AreEqual(18, dt.Age());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DateTimeExtensions.First"/>.
+        /// </summary>
+        [TestMethod]
+        public void First()
+        {
+            var dt = new DateTime(2018, 6, 20);
+
+            Assert.AreEqual(4, dt.First(DayOfWeek.Monday).Day);
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DateTimeExtensions.FirstDayOfMonth"/>.
+        /// </summary>
+        [TestMethod]
+        public void FirstDayOfMonth()
+        {
+            var dt = new DateTime(2018, 6, 20);
+            DateTime first = dt.FirstDayOfMonth();
+
+            Assert.AreEqual(dt.Year, first.Year);
+            Assert.AreEqual(dt.Month, first.Month);
+            Assert.AreEqual(1, first.Day);
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DateTimeExtensions.Last"/>.
+        /// </summary>
+        [TestMethod]
+        public void Last()
+        {
+            {
+                var dt = new DateTime(2019, 12, 1);
+                DateTime last = dt.Last(DayOfWeek.Wednesday);
+
+                Assert.AreEqual(dt.Year, last.Year);
+                Assert.AreEqual(dt.Month, last.Month);
+                Assert.AreEqual(25, last.Day);
+            }
+
+            {
+                var dt = new DateTime(2020, 4, 14);
+                DateTime last = dt.Last(DayOfWeek.Friday);
+
+                Assert.AreEqual(dt.Year, last.Year);
+                Assert.AreEqual(dt.Month, last.Month);
+                Assert.AreEqual(24, last.Day);
+
+                last = dt.Last(DayOfWeek.Thursday);
+                Assert.AreEqual(dt.Year, last.Year);
+                Assert.AreEqual(dt.Month, last.Month);
+                Assert.AreEqual(30, last.Day);
+            }
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DateTimeExtensions.LastDayOfMonth"/>.
+        /// </summary>
+        [TestMethod]
+        public void LastDayOfMonth()
+        {
+            var dt = new DateTime(2016, 2, 4);
+            DateTime last = dt.LastDayOfMonth();
+
+            Assert.AreEqual(dt.Year, last.Year);
+            Assert.AreEqual(dt.Month, last.Month);
+            Assert.AreEqual(29, last.Day); // 2016 is a leap year
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DateTimeExtensions.ToUnixTimeStamp"/>.
+        /// </summary>
+        [TestMethod]
+        public void ToUnixTimestamp()
+        {
+            var dt = new DateTime(2015, 10, 21, 1, 0, 0, DateTimeKind.Utc);
+            var unix = dt.ToUnixTimeStamp();
+
+            Assert.AreEqual(1445389200L, unix);
+        }
+    }
+}
diff --git a/X10D.Tests/src/DictionaryTests.cs b/X10D.Tests/src/DictionaryTests.cs
new file mode 100644
index 0000000..e85b895
--- /dev/null
+++ b/X10D.Tests/src/DictionaryTests.cs
@@ -0,0 +1,42 @@
+namespace X10D.Tests
+{
+    using System.Collections.Generic;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="DictionaryExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class DictionaryTests
+    {
+        /// <summary>
+        /// Tests for <see cref="DictionaryExtensions.ToConnectionString{T1,T2}(IDictionary{T1,T2})"/>.
+        /// </summary>
+        [TestMethod]
+        public void ToConnectionString()
+        {
+            var dictionary = new Dictionary<string, object>
+            {
+                { "username", "Foo" }, { "password", "Foo Bar" }, { "port", 3306 },
+            };
+
+            var connectionString = dictionary.ToConnectionString();
+            Assert.AreEqual("username=Foo;password=\"Foo Bar\";port=3306", connectionString);
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DictionaryExtensions.ToGetParameters{T1,T2}(IDictionary{T1,T2})"/>.
+        /// </summary>
+        [TestMethod]
+        public void ToGetParameters()
+        {
+            var dictionary = new Dictionary<string, object>
+            {
+                { "username", "Foo" }, { "password", "Foo Bar" }, { "port", 3306 },
+            };
+
+            var getParameterString = dictionary.ToGetParameters();
+            Assert.AreEqual("username=Foo&password=Foo+Bar&port=3306", getParameterString);
+        }
+    }
+}
diff --git a/X10D.Tests/src/DoubleTests.cs b/X10D.Tests/src/DoubleTests.cs
new file mode 100644
index 0000000..9f7a25a
--- /dev/null
+++ b/X10D.Tests/src/DoubleTests.cs
@@ -0,0 +1,84 @@
+namespace X10D.Tests
+{
+    using System;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="DoubleExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class DoubleTests
+    {
+        /// <summary>
+        /// Tests for <see cref="DoubleExtensions.Clamp"/>.
+        /// </summary>
+        [TestMethod]
+        public void Clamp()
+        {
+            Assert.AreEqual(2.0, 3.0.Clamp(1.0, 2.0));
+            Assert.AreEqual(1.0, (-3.0).Clamp(1.0, 2.0));
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DoubleExtensions.DegreesToRadians"/>.
+        /// </summary>
+        [TestMethod]
+        public void DegreesToRadians()
+        {
+            Assert.AreEqual(Math.PI, 180.0.DegreesToRadians());
+            Assert.AreEqual(Math.PI * 1.5, 270.0.DegreesToRadians());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DoubleExtensions.GetBytes"/>.
+        /// </summary>
+        [TestMethod]
+        public void GetBytes()
+        {
+            CollectionAssert.AreEqual(
+                new byte[] { 0x18, 0x2D, 0x44, 0x54, 0xFB, 0x21, 0x09, 0x40 },
+                Math.PI.GetBytes());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DoubleExtensions.IsEven"/>.
+        /// </summary>
+        [TestMethod]
+        public void IsEven()
+        {
+            Assert.IsTrue(2.0.IsEven());
+            Assert.IsFalse(1.0.IsEven());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DoubleExtensions.IsOdd"/>.
+        /// </summary>
+        [TestMethod]
+        public void IsOdd()
+        {
+            Assert.IsFalse(2.0.IsOdd());
+            Assert.IsTrue(1.0.IsOdd());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DoubleExtensions.RadiansToDegrees"/>.
+        /// </summary>
+        [TestMethod]
+        public void RadiansToDegrees()
+        {
+            Assert.AreEqual(180.0, Math.PI.RadiansToDegrees());
+            Assert.AreEqual(360.0, (2.0 * Math.PI).RadiansToDegrees());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="DoubleExtensions.Round"/>.
+        /// </summary>
+        [TestMethod]
+        public void Round()
+        {
+            Assert.AreEqual(5.0, 3.5.Round(5));
+            Assert.AreEqual(5.0, 7.0.Round(5));
+            Assert.AreEqual(10.0, 7.5.Round(5));
+        }
+    }
+}
diff --git a/X10D.Tests/src/EnumerableTests.cs b/X10D.Tests/src/EnumerableTests.cs
new file mode 100644
index 0000000..c87ef8a
--- /dev/null
+++ b/X10D.Tests/src/EnumerableTests.cs
@@ -0,0 +1,55 @@
+namespace X10D.Tests
+{
+    using System.Collections.Generic;
+    using System.Linq;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    /// <summary>
+    /// Tests for <see cref="EnumerableExtensions"/>.
+    /// </summary>
+    [TestClass]
+    public class EnumerableTests
+    {
+        /// <summary>
+        /// Tests for <see cref="EnumerableExtensions.Split{T}"/> using an array of <see cref="byte"/>.
+        /// </summary>
+        [TestMethod]
+        public void SplitByte()
+        {
+            byte[] foo = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08 };
+            IEnumerable<IEnumerable<byte>> chunks = foo.Split(2).ToArray();
+
+            Assert.AreEqual(4, chunks.Count());
+            CollectionAssert.AreEqual(new byte[] { 0x01, 0x02 }, chunks.ElementAt(0).ToList());
+            CollectionAssert.AreEqual(new byte[] { 0x03, 0x04 }, chunks.ElementAt(1).ToList());
+            CollectionAssert.AreEqual(new byte[] { 0x05, 0x06 }, chunks.ElementAt(2).ToList());
+            CollectionAssert.AreEqual(new byte[] { 0x07, 0x08 }, chunks.ElementAt(3).ToList());
+
+            // test exceeding chunk size
+            chunks = foo.Split(foo.Length + 10).ToArray();
+            Assert.AreEqual(1, chunks.Count());
+            CollectionAssert.AreEqual(foo, chunks.SelectMany(c => c).ToList());
+        }
+
+        /// <summary>
+        /// Tests for <see cref="EnumerableExtensions.Split{T}"/> using an array of <see cref="int"/>.
+        /// </summary>
+        [TestMethod]
+        public void SplitInt32()
+        {
+            int[] foo = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08 };
+            IEnumerable<IEnumerable<int>> chunks = foo.Split(2).ToArray();
+
+            Assert.AreEqual(4, chunks.Count());
+            CollectionAssert.AreEqual(new[] { 0x01, 0x02 }, chunks.ElementAt(0).ToList());
+            CollectionAssert.AreEqual(new[] { 0x03, 0x04 }, chunks.ElementAt(1).ToList());
+            CollectionAssert.AreEqual(new[] { 0x05, 0x06 }, chunks.ElementAt(2).ToList());
+            CollectionAssert.AreEqual(new[] { 0x07, 0x08 }, chunks.ElementAt(3).ToList());
+
+            // test exceeding chunk size
+            chunks = foo.Split(foo.Length + 10).ToArray();
+            Assert.AreEqual(1, chunks.Count());
+            CollectionAssert.AreEqual(foo, chunks.SelectMany(c => c).ToList());
+        }
+    }
+}
diff --git a/X10D.Tests/src/TimeSpanParserTests.cs b/X10D.Tests/src/TimeSpanParserTests.cs
new file mode 100644
index 0000000..452a3a1
--- /dev/null
+++ b/X10D.Tests/src/TimeSpanParserTests.cs
@@ -0,0 +1,20 @@
+namespace X10D.Tests
+{
+    using System;
+    using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+    [TestClass]
+    public class TimeSpanParserTests
+    {
+        [TestMethod]
+        public void TestParser()
+        {
+            Assert.AreEqual(TimeSpan.FromHours(3), "3h".ToTimeSpan());
+            Assert.AreEqual(TimeSpan.FromMinutes(2.5), "2.5m".ToTimeSpan());
+            Assert.AreEqual(TimeSpan.FromHours(1), "60m".ToTimeSpan());
+            Assert.AreEqual(TimeSpan.FromDays(1), "1d".ToTimeSpan());
+            Assert.AreEqual(TimeSpan.FromDays(8), "1w 1d".ToTimeSpan());
+            Assert.AreEqual(TimeSpan.FromDays(8), "1w1d".ToTimeSpan());
+        }
+    }
+}