Codebasis als Dateien ins Arbeitsrepo statt als Gitlink

QuellCode/CentronERP war nur als Gitlink (Submodul-Referenz auf 79c1142)
getrackt, ohne .gitmodules und ohne erreichbares Remote. Der
Untersuchungsgegenstand der Versuchsreihe war damit nicht reproduzierbar
gesichert: Ein Klon haette ein leeres Verzeichnis erhalten, und die Belege
der 3.287 Anforderungen waeren nicht ueberpruefbar gewesen.

Umstellung:
- Historie nach c:\DEV\CentronERP_git_snapshot_79c1142 ausgelagert
  (vollstaendig lesbar, enthaelt 79c1142 und Vorgaenger 89ccfd6)
- Gitlink aus dem Index entfernt
- Dateiinhalt aufgenommen: 24.557 Dateien, rund 333 MB

Die verschachtelte .gitignore der Codebasis gilt weiter, Build-Artefakte
bleiben ausgeschlossen. Details in Versuche/Versuch_01/_Codebasis-Nachweis.md

QuellCode/CentronERP/tests/shared/Centron.Tests.Core/Centron.Tests.Core.csproj

@@ -0,0 +1,36 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="coverlet.collector" Version="10.0.0">
+          <PrivateAssets>all</PrivateAssets>
+          <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+        <PackageReference Include="JetBrains.Annotations" Version="2025.2.4" />
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
+        <PackageReference Include="NSubstitute" Version="5.3.0" />
+        <PackageReference Include="System.Data.SQLite" Version="1.0.119" />
+        <!-- Override vulnerable transitive dependencies -->
+        <PackageReference Include="System.Drawing.Common" Version="10.0.7" />
+        <PackageReference Include="System.Data.SqlClient" Version="4.9.1" />
+        <PackageReference Include="xunit" Version="2.9.3" />
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5" />
+    </ItemGroup>
+
+    <ItemGroup>
+        <Using Include="Xunit" />
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\..\src\shared\Centron.Core\Centron.Core.csproj" />
+    </ItemGroup>
+</Project>

QuellCode/CentronERP/tests/shared/Centron.Tests.Core/Extensions/StringExtensionsTest.cs

@@ -0,0 +1,44 @@
+using JetBrains.Annotations;
+
+namespace Centron.Core.Extensions;
+
+[TestSubject(typeof(StringExtensions))]
+public class StringExtensionsTest
+{
+    [Theory]
+    [InlineData("", "")]
+    [InlineData(null, "")]
+    [InlineData("test\r\ntest", "test test")]
+    [InlineData("test\ntest", "test test")]
+    [InlineData("test test", "test test")]
+    public void TestMakeOneLiner(string? input, string expected)
+    {
+        var result = input.MakeOneLiner();
+        Assert.Equal(expected, result);
+    }
+    
+    [Theory]
+    [InlineData("", null)]
+    [InlineData(null, null)]
+    [InlineData("\n", null)]
+    [InlineData("\r\n", null)]
+    [InlineData("\n\n", null)]
+    [InlineData("\r\n\r\n", null)]
+    [InlineData("\r\n \r\n ", null)]
+    [InlineData("\n \n ", null)]
+    [InlineData(" ", null)]
+    [InlineData("First line\nSecond line", "First line")]
+    [InlineData("First line\r\nSecond line", "First line")]
+    [InlineData(" \r\nFirst line", "First line")]
+    [InlineData(" \nFirst line", "First line")]
+    [InlineData("\r\n\r\nFirst line", "First line")]
+    [InlineData("\n\nFirst line", "First line")]
+    [InlineData("Single line text", "Single line text")]
+    [InlineData("\nStarts with newline", "Starts with newline")]
+    [InlineData("\r\nStarts with newline", "Starts with newline")]
+    public void TestTakeFirstLine(string? input, string? expected)
+    {
+        var result = input.TakeFirstLine();
+        Assert.Equal(expected, result);
+    }
+}