Add test for rewording a merge commit

This currently fails with an error.

pkg/integration/tests/interactive_rebase/reword_merge_commit.go

@@ -0,0 +1,56 @@
+package interactive_rebase
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var RewordMergeCommit = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Rewords a merge commit which is not the current head commit",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.
+			EmptyCommit("base").
+			NewBranch("first-branch").
+			CreateFileAndAdd("file1.txt", "content").
+			Commit("one").
+			Checkout("master").
+			Merge("first-branch").
+			NewBranch("second-branch").
+			EmptyCommit("two")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			Lines(
+				Contains("CI ◯ two").IsSelected(),
+				Contains("CI ⏣─╮ Merge branch 'first-branch'"),
+				Contains("CI │ ◯ one"),
+				Contains("CI ◯─╯ base"),
+			).
+			SelectNextItem().
+			Press(keys.Commits.RenameCommit).
+			Tap(func() {
+				t.ExpectPopup().CommitMessagePanel().
+					Title(Equals("Reword commit")).
+					InitialText(Equals("Merge branch 'first-branch'")).
+					Clear().
+					Type("renamed merge").
+					Confirm()
+			}).
+			/* EXPECTED:
+			Lines(
+				Contains("CI ◯ two"),
+				Contains("CI ⏣─╮ renamed merge").IsSelected(),
+				Contains("CI │ ◯ one"),
+				Contains("CI ◯ ╯ base"),
+			)
+			ACTUAL: */
+			Tap(func() {
+				t.ExpectPopup().Alert().Title(Equals("Error")).
+					Content(Contains("error: 'edit' does not accept merge commits"))
+			})
+	},
+})

pkg/integration/tests/test_list.go

@@ -275,6 +275,7 @@ var tests = []*components.IntegrationTest{
 	interactive_rebase.RewordFirstCommit,
 	interactive_rebase.RewordLastCommit,
 	interactive_rebase.RewordLastCommitOfStackedBranch,
+	interactive_rebase.RewordMergeCommit,
 	interactive_rebase.RewordYouAreHereCommit,
 	interactive_rebase.RewordYouAreHereCommitWithEditor,
 	interactive_rebase.ShowExecTodos,