Add command to paste commit message from clipboard

Resolves #3672

pkg/integration/tests/commit/paste_commit_message_over_existing.go

@@ -0,0 +1,54 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var PasteCommitMessageOverExisting = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Paste a commit message into the commit message panel when there is already text in the panel, causing a confirmation",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig: func(config *config.AppConfig) {
+		config.UserConfig.OS.CopyToClipboardCmd = "echo {{text}} > ../clipboard"
+		config.UserConfig.OS.ReadFromClipboardCmd = "cat ../clipboard"
+	},
+	SetupRepo: func(shell *Shell) {
+		shell.EmptyCommit("subject\n\nbody 1st line\nbody 2nd line")
+		shell.CreateFileAndAdd("file", "file content")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Focus().
+			ContainsLines(
+				Contains("subject").IsSelected(),
+			).
+			Press(keys.Commits.CopyCommitAttributeToClipboard)
+
+		t.ExpectPopup().Menu().Title(Equals("Copy to clipboard")).
+			Select(Contains("Commit message")).Confirm()
+
+		t.ExpectToast(Equals("Commit message copied to clipboard"))
+
+		t.Views().Files().
+			Focus().
+			Press(keys.Files.CommitChanges)
+
+		t.ExpectPopup().CommitMessagePanel().
+			Type("existing message").
+			OpenCommitMenu()
+
+		t.ExpectPopup().Menu().Title(Equals("Commit Menu")).
+			Select(Contains("Paste commit message from clipboard")).
+			Confirm()
+
+		t.ExpectPopup().Alert().Title(Equals("Paste commit message from clipboard")).
+			Content(Equals("Pasting will overwrite the current commit message, continue?")).
+			Confirm()
+
+		t.ExpectPopup().CommitMessagePanel().
+			Content(Equals("subject")).
+			SwitchToDescription().
+			Content(Equals("body 1st line\nbody 2nd line"))
+	},
+})