Add unit test project

TwitchDownloaderTests/GlobalUsings.cs

@@ -0,0 +1 @@
+global using Xunit;

TwitchDownloaderTests/TwitchDownloaderTests.csproj

@@ -0,0 +1,29 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFrameworks>net6.0;net6.0-windows</TargetFrameworks>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.1" />
+        <PackageReference Include="xunit" Version="2.6.1" />
+        <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3">
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+            <PrivateAssets>all</PrivateAssets>
+        </PackageReference>
+        <PackageReference Include="coverlet.collector" Version="3.2.0">
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+            <PrivateAssets>all</PrivateAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+      <ProjectReference Include="..\TwitchDownloaderCore\TwitchDownloaderCore.csproj" />
+    </ItemGroup>
+
+</Project>

TwitchDownloaderWPF.sln

@@ -9,6 +9,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TwitchDownloaderCore", "Twi
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TwitchDownloaderCLI", "TwitchDownloaderCLI\TwitchDownloaderCLI.csproj", "{F14A9B02-36A4-4FFF-9AD0-7475E2CF2D5C}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TwitchDownloaderTests", "TwitchDownloaderTests\TwitchDownloaderTests.csproj", "{FE8F0DC2-6750-4956-9208-9CEE9B524184}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -41,6 +43,14 @@ Global
 		{F14A9B02-36A4-4FFF-9AD0-7475E2CF2D5C}.Release|Any CPU.Build.0 = Release|Any CPU
 		{F14A9B02-36A4-4FFF-9AD0-7475E2CF2D5C}.Release|x64.ActiveCfg = Release|x64
 		{F14A9B02-36A4-4FFF-9AD0-7475E2CF2D5C}.Release|x64.Build.0 = Release|x64
+		{FE8F0DC2-6750-4956-9208-9CEE9B524184}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{FE8F0DC2-6750-4956-9208-9CEE9B524184}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{FE8F0DC2-6750-4956-9208-9CEE9B524184}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{FE8F0DC2-6750-4956-9208-9CEE9B524184}.Debug|x64.Build.0 = Debug|Any CPU
+		{FE8F0DC2-6750-4956-9208-9CEE9B524184}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{FE8F0DC2-6750-4956-9208-9CEE9B524184}.Release|Any CPU.Build.0 = Release|Any CPU
+		{FE8F0DC2-6750-4956-9208-9CEE9B524184}.Release|x64.ActiveCfg = Release|Any CPU
+		{FE8F0DC2-6750-4956-9208-9CEE9B524184}.Release|x64.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE