Add test for a special situation in rebases involving empty commits

The situation is that you perform a rebase, and one of the commits becomes empty
during the rebase, in a way that couldn't be predicted before the rebase
started. To explain: git rebase has some logic where it immediately discards
commits if it can tell that they already exist in the branch being rebased onto;
it does this by looking at the patch ids of the commits to work out which
commits already exist upstream. But for those commits that become empty even
though there isn't a corresponding commit upstream, git stops with an error, and
lazygit detects this (in CheckMergeOrRebaseWithRefreshOptions) and automatically
continues the rebase.

This all works fine; I'm adding this test because I almost broke this during
development of this branch, so I'm adding it to guard against regressions.

Author: stefanhaller

pkg/integration/tests/interactive_rebase/rebase_with_commit_that_becomes_empty.go

@@ -0,0 +1,45 @@
+package interactive_rebase
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var RebaseWithCommitThatBecomesEmpty = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Performs a rebase involving a commit that becomes empty during the rebase, and gets dropped.",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.EmptyCommit("initial commit")
+		// It is important that we create two separate commits for the two
+		// changes to the file, but only one commit for the same changes on our
+		// branch; otherwise, the commit would be discarded at the start of the
+		// rebase already.
+		shell.CreateFileAndAdd("file", "change 1\n")
+		shell.Commit("master change 1")
+		shell.UpdateFileAndAdd("file", "change 1\nchange 2\n")
+		shell.Commit("master change 2")
+		shell.NewBranchFrom("branch", "HEAD^^")
+		shell.CreateFileAndAdd("file", "change 1\nchange 2\n")
+		shell.Commit("branch change")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Branches().
+			Focus().
+			NavigateToLine(Contains("master")).
+			Press(keys.Branches.RebaseBranch)
+
+		t.ExpectPopup().Menu().
+			Title(Equals("Rebase 'branch'")).
+			Select(Contains("Simple rebase")).
+			Confirm()
+
+		t.Views().Commits().
+			Lines(
+				Contains("master change 2"),
+				Contains("master change 1"),
+				Contains("initial commit"),
+			)
+	},
+})

pkg/integration/tests/test_list.go

@@ -260,6 +260,7 @@ var tests = []*components.IntegrationTest{
 	interactive_rebase.QuickStartKeepSelection,
 	interactive_rebase.QuickStartKeepSelectionRange,
 	interactive_rebase.Rebase,
+	interactive_rebase.RebaseWithCommitThatBecomesEmpty,
 	interactive_rebase.RewordCommitWithEditorAndFail,
 	interactive_rebase.RewordFirstCommit,
 	interactive_rebase.RewordLastCommit,