Add integration test

pkg/integration/components/commit_message_panel_driver.go

@@ -74,6 +74,10 @@ func (self *CommitMessagePanelDriver) Cancel() {
 	self.getViewDriver().PressEscape()
 }
 
+func (self *CommitMessagePanelDriver) SwitchToEditor() {
+	self.getViewDriver().Press(self.t.keys.CommitMessage.SwitchToEditor)
+}
+
 func (self *CommitMessagePanelDriver) SelectPreviousMessage() *CommitMessagePanelDriver {
 	self.getViewDriver().SelectPreviousItem()
 	return self

pkg/integration/tests/commit/commit_switch_to_editor.go

@@ -0,0 +1,54 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var CommitSwitchToEditor = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Commit, then switch from built-in commit message panel to editor",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateFile("file1", "file1 content")
+		shell.CreateFile("file2", "file2 content")
+
+		// Set an editor that appends a line to the existing message. Since
+		// git adds all this "# Please enter the commit message for your changes"
+		// stuff, this will result in an extra blank line before the added line.
+		shell.SetConfig("core.editor", "sh -c 'echo third line >>.git/COMMIT_EDITMSG'")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			IsEmpty()
+
+		t.Views().Files().
+			IsFocused().
+			PressPrimaryAction(). // stage one of the files
+			Press(keys.Files.CommitChanges)
+
+		t.ExpectPopup().CommitMessagePanel().
+			Type("first line").
+			SwitchToDescription().
+			Type("second line").
+			SwitchToSummary().
+			SwitchToEditor()
+		t.Views().Commits().
+			Lines(
+				Contains("first line"),
+			)
+
+		t.Views().Commits().Focus()
+		t.Views().Main().Content(MatchesRegexp(`first line\n\s*\n\s*second line\n\s*\n\s*third line`))
+
+		// Now check that the preserved commit message was cleared:
+		t.Views().Files().
+			Focus().
+			PressPrimaryAction(). // stage the other file
+			Press(keys.Files.CommitChanges)
+
+		t.ExpectPopup().CommitMessagePanel().
+			InitialText(Equals(""))
+	},
+})

pkg/integration/tests/test_list.go

@@ -55,6 +55,7 @@ var tests = []*components.IntegrationTest{
 	commit.Amend,
 	commit.Commit,
 	commit.CommitMultiline,
+	commit.CommitSwitchToEditor,
 	commit.CommitWipWithPrefix,
 	commit.CommitWithPrefix,
 	commit.CreateTag,