Add a reduced demo test

Author: bitbonk

src/GitVersion.Core.Tests/IntegrationTests/ReducedReleaseWorkflowDemo.cs

@@ -0,0 +1,103 @@
+using GitTools.Testing;
+using GitVersion.Model.Configuration;
+using LibGit2Sharp;
+using NUnit.Framework;
+using Shouldly;
+
+namespace GitVersion.Core.Tests.IntegrationTests;
+
+public class ReducedReleaseWorkflowDemo : IDisposable
+{
+    private static readonly EmptyRepositoryFixture _fixture = new();
+
+    private static readonly Config _config = new()
+    {
+        // ❓ In my GitVersion.yml I actually have set the version to "1.0"
+        // but that will cause an exception when I do it here in the tests
+        NextVersion = "1.0.0"
+    };
+
+    public void Dispose() => _fixture.Dispose();
+
+    [Test]
+    public void Demo()
+    {
+        // create main and develop branches
+        // develop is one commits ahead of main
+        MakeACommit();
+        CreateAndCheckoutBranch("develop");
+        MakeACommit();
+
+        // ✅ succeeds as expected
+        GetCurrentSemVer().ShouldBe("1.0.0-alpha.1");
+
+        // now we are ready to start with the preparation of the 1.0.0 release
+        CreateAndCheckoutBranch("release/1.0.0");
+
+        // ✅ succeeds as expected
+        GetCurrentSemVer().ShouldBe("1.0.0-beta.1");
+
+        // make another commit on release/1.0.0 to prepare the actual beta1 release
+        MakeACommit();
+
+        // ✅ succeeds as expected
+        GetCurrentSemVer().ShouldBe("1.0.0-beta.1");
+
+        // now we makes changes on develop that may or may not end up in the 1.0.0 release
+        CheckoutBranch("develop");
+        MakeACommit();
+
+        // ❌ fails! actual: "1.1.0-alpha.1"
+        // We have not released 1.0.0, not even a beta, so why increment to 1.1.0?
+        // Even though this surprising, it might actually be OK,
+        // at least the version is incremented, which is needed for the CI nuget feed
+        GetCurrentSemVer().ShouldBe("1.0.0-alpha.2");
+
+        // now we do the actual release of beta 1
+        CheckoutBranch("release/1.0.0");
+        ApplyTag("1.0.0-beta1");
+
+        // ✅ succeeds as expected
+        GetCurrentSemVer().ShouldBe("1.0.0-beta.1");
+
+        // continue with more work on develop that may or may not end up in the 1.0.0 release
+        CheckoutBranch("develop");
+        MakeACommit();
+
+        // ❌ fails! actual: "1.1.0-alpha.2"
+        // We still have not finally released 1.0.0 yet, only a beta, so why increment to 1.1.0?
+        // Even though this surprising, it might actually be OK,
+        // at least the version is incremented, which is needed for the CI nuget feed
+        GetCurrentSemVer().ShouldBe("1.0.0-alpha.3");
+
+        // now we decide that the new changes on develop should be part of the beta 2 release
+        // se we merge it into release/1.0.0 with --no-ff because it is a protected branch
+        // but we don't do the release of beta 2 jus yet
+        CheckoutBranch("release/1.0.0");
+        MergeWithNoFF("develop");
+
+        // ✅ succeeds as expected
+        GetCurrentSemVer().ShouldBe("1.0.0-beta.2");
+
+        CheckoutBranch("develop");
+
+        // ❌ fails! actual "1.0.0-alpha.3"
+        // This is now really a problem. Why did it decrement the minor version?
+        // All subsequent changes on develop will now a lower version that previously
+        // and the nuget packages end up on the CI feed with a lower version
+        // so users of that feed would need to _downgrade_ to get a _newer_ version.
+        GetCurrentSemVer().ShouldBe("1.1.0-alpha.2");
+    }
+
+    private static void MakeACommit() => _fixture.Repository.MakeACommit();
+
+    private void CheckoutBranch(string branchName) => Commands.Checkout(_fixture.Repository, _fixture.Repository.Branches[branchName]);
+
+    private void CreateAndCheckoutBranch(string branchName) => Commands.Checkout(_fixture.Repository, _fixture.Repository.CreateBranch(branchName));
+
+    private string GetCurrentSemVer() => _fixture.GetVersion(_config).SemVer;
+
+    private void ApplyTag(string tag) => _fixture.Repository.ApplyTag(tag);
+
+    private void MergeWithNoFF(string sourceBranch) => _fixture.Repository.MergeNoFF(sourceBranch);
+}