Add test for amending a merge commit

pkg/integration/components/shell.go

@@ -64,7 +64,7 @@ func (s *Shell) Checkout(name string) *Shell {
 }
 
 func (s *Shell) Merge(name string) *Shell {
-	return s.RunCommand("git merge --commit " + name)
+	return s.RunCommand("git merge --commit --no-ff " + name)
 }
 
 func (s *Shell) GitAdd(path string) *Shell {

pkg/integration/tests/interactive_rebase/amend_merge.go

@@ -0,0 +1,37 @@
+package interactive_rebase
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var AmendMerge = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Amends a staged file to a merge commit.",
+	ExtraCmdArgs: "",
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.
+			NewBranch("development-branch").
+			CreateFileAndAdd("initial-file", "content").
+			Commit("initial commit").
+			NewBranch("feature-branch"). // it's also checked out automatically
+			CreateFileAndAdd("new-feature-file", "new content").
+			Commit("new feature commit").
+			CheckoutBranch("development-branch").
+			Merge("feature-branch").
+			CreateFileAndAdd("post-merge-file", "content")
+	},
+	Run: func(shell *Shell, input *Input, assert *Assert, keys config.KeybindingConfig) {
+		assert.CommitCount(3)
+
+		input.SwitchToCommitsWindow()
+		assert.CurrentViewName("commits")
+
+		input.PressKeys(keys.Commits.AmendToCommit)
+		input.PressKeys(keys.Universal.Return)
+
+		assert.MatchHeadCommitMessage(Contains("Merge"))
+		assert.CommitCount(3)
+	},
+})

pkg/integration/tests/tests.go

@@ -29,6 +29,7 @@ var tests = []*components.IntegrationTest{
 	branch.Rebase,
 	branch.RebaseAndDrop,
 	interactive_rebase.One,
+	interactive_rebase.AmendMerge,
 	custom_commands.Basic,
 	custom_commands.MultiplePrompts,
 	custom_commands.MenuFromCommand,