Add new integration tests folder "shell_commands"

The folder custom_commands contained tests for both custom commands (the ones
you configure in config.yml) and shell commands (the ones you execute at the ":"
prompt). I always found this confusing, so separate these into two different
folders.

pkg/integration/tests/shell_commands/complex_shell_command.go

@@ -0,0 +1,35 @@
+package shell_commands
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var ComplexShellCommand = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Using a custom command provided at runtime to create a new file, via a shell command. We invoke custom commands through a shell already. This test proves that we can run a shell within a shell, which requires complex escaping.",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupRepo: func(shell *Shell) {
+		shell.EmptyCommit("blah")
+	},
+	SetupConfig: func(cfg *config.AppConfig) {},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsEmpty().
+			IsFocused().
+			Press(keys.Universal.ExecuteCustomCommand)
+
+		t.ExpectPopup().Prompt().
+			Title(Equals("Custom command:")).
+			Type("sh -c \"touch file.txt\"").
+			Confirm()
+
+		t.GlobalPress(keys.Files.RefreshFiles)
+
+		t.Views().Files().
+			IsFocused().
+			Lines(
+				Contains("file.txt"),
+			)
+	},
+})