catwalk is a unit test library for Bubbletea TUI models (a.k.a. “bubbles”).

It enables implementers to verify the state of models and their View as they process tea.Msg objects through their Update method.

It is implemented on top of datadriven, an extension to Go's simple "table-driven testing" idiom.

Datadriven tests use data files containing both the reference input and output, instead of a data structure. Each data file can contain multiple tests. When the implementation changes, the reference output can be quickly updated by re-running the tests with the -rewrite flag.

Why the name: the framework forces the Tea models to "show themselves" on the runway of the test input files.

Let's test the viewport Bubble!

First, we define a top-level model around viewport:

type Model struct {
    viewport.Model
}

var _ tea.Model = (*Model)(nil)

// New initializes a new model.
func New(width, height int) *Model {
    return &Model{
        Model: viewport.New(width, height),
    }
}

// Init adds some initial text inside the viewport.
func (m *Model) Init() tea.Cmd {
    cmd := m.Model.Init()
    m.SetContent(`first line
second line
third line
fourth line
fifth line
sixth line`)
    return cmd
}

Then, we define a Go test which runs the above model:

func TestModel(t *testing.T) {
	// Initialize the model to test.
	m := New(40, 3)

    // Run all the tests in input file "testdata/viewport_tests"
	catwalk.RunModel(t, "testdata/viewport_tests", m)
}

Then, we populate some test directives inside testdata/viewport_tests:

run
----

# One line down
run
type j
----

# Two lines down
run
type jj
----

# One line up
run
key up
----

Then, we run the test: go test ..

What happens: the test fails!

--- FAIL: TestModel (0.00s)
    catwalk.go:64:
        testdata/viewport_tests:1:
        expected:

        found:
        -- view:
        first line␤
        second line␤
        third line🛇

This is because we haven't yet expressed what is the expected output for each step.

Because it's tedious to do this manually, we can auto-generate the expected output from the actual output, using the rewrite flag:

 go test . -args -rewrite

Observe what happened with the input file:

run
----
-- view:
first line␤
second line␤
third line🛇

# One line down
run
type j
----
-- view:
second line␤
third line␤
fourth line🛇

# Two lines down
run
type jj
----
-- view:
fourth line␤
fifth line␤
sixth line🛇

# One line up
run
key up
----
-- view:
third line␤
fourth line␤
fifth line🛇

Now each expected output reflects how the viewport reacts to the key presses. Now also go test . succeeds.

Test files contain zero or more tests, with the following structure:

<directive> <arguments>
<optional: input commands...>
----
<expected output>

For example:

run
----
-- view:
My bubble rendered here.

run
type q
----
-- view:
My bubble reacted to "q".

Catwalk supports the following directives:

• run: apply state changes to the model via its Update method, then show the results.
• set/reset: change configuration variables.

Finally, directives can take arguments. For example:

run observe=(gostruct,view)
----

This is explained further in the next sections.

run defines one unit test. It applies some input commands to the model then compares the resulting state of the model with a reference expected output.

Under run, the following input commands are supported:

• type <text>: produce a series of tea.KeyMsg with type tea.KeyRunes. Can contain spaces.

  For example: type abc produces 3 key presses for a, b, c.

• enter <text>: like type, but also add a key press for the enter key at the end.

• key <keyname>: produce one tea.KeyMsg for the given key.

  For example: key ctrl+c

• paste "<text>": paste the text as a single key event. The text can contain Go escape sequences.

  For example: paste "hello\nworld"

• resize <W> <H>: produce a tea.WindowSizeMsg with the specified size.

You can also add support for your own input commands by passing an Updater function to catwalk.RunModel with the WithUpdater() option, and combine multiple updaters together using the ChainUpdater() function.

The run directive accepts the following arguments:

• observe: what to look at as expected output (observe=xx or observe=(xx,yy)).

  By default, observe is set to view: look at the model's View() method. Alternatively, you can use the following observers:

  • gostruct: show the contents of the model object as a go struct.
  • debug: call the model's Debug() string method, if defined.

  You can also add your own observers using the WithObserver() option.

• trace: detail the intermediate steps of the test.

  Used for debugging tests.

These can be used to configure parameters in the test driver.

For example:

set cmd_timeout=100ms
----
cmd_timeout: 100ms

reset cmd_timeout
----
ok

The following parameters are currently recognized:

• cmd_timeout: how long to wait for a tea.Cmd to complete. This is set by default to 20ms, which is sufficient to ignore the commands of a blinking cursor.

Many bubbles have a Styles struct with configurable styles (using lipgloss). It's useful to verify that the bubbles react properly when the styles are reconfigured at run-time.

For this, you can tell catwalk about your styles this will activate the following special run input commands:

restyle <stylefield> <newstyle...>`

For example: restyle mymodel.ValueStyle foreground: #f00 changes the ValueStyle style to use the color red, as if .ValueStyle.Foreground(lipgloss.Color("#f00")) was called.

To activate, use the option catwalk.WithUpdater(catwalk.StylesUpdater(...)). For example:

func TestStyles(t *testing.T) {
  m := New(...)
  catwalk.RunModel(t, "testdata/styles", m, catwalk.WithUpdater(
    // The string "hello" is the prefix for identifying the styles container in tests.
    // Useful when there are multiple nested models.
    catwalk.StylesUpdater("hello",
      func(m tea.Model, fn func(interface{}) error) (tea.Model, error) {
        tm := m.(myModel)
        err := fn(&tm)
        return tm, err
    }),
  ))
}

After this, the input command restyle hello.X ... will automatically affect the style .X in your model.

Alternatively, if your model implements tea.Model by reference (i.e. the address of its styles does not change between Update calls), you can simplify as follows:

func TestStyles(t *testing.T) {
  m := New(...)
  catwalk.RunModel(t, "testdata/bindings", &m, catwalk.WithUpdater(
    // The string "hello" is the prefix for identifying the styles container in tests.
    // Useful when there are multiple nested models.
    KeyMapUpdater("hello", catwalk.SimpleStylesApplier(&m))))
}

See the test TestStyles in styles_test.go and the input file testdata/styles for an example.

Many bubbles have a KeyMap struct with configurable key bindings. It's useful to verify that the bubbles react properly when the keymaps are reconfigured at run-time.

For this, you can tell catwalk about your KeyMap struct and this will activate the following special run input commands:

• keybind <keymapfield> <newbinding>

  For example: keybind mykeys.CursorUp up j rebinds the CursorUp binding in the KeyMap mykeys as if key.NewBinding(key.WithKeys("up", "j")) was called.

• keyhelp <keymapfield> <helpkey> <helptext>

  For example: keybind mykeys.CursorUp up move the cursor up rebinds the CursorUp binding in the KeyMap mykeys as if key.NewBinding(key.WithHelp("up", "move the cursor up")) was called.

To declare a KeyMap in a test, use the option catwalk.WithUpdater(catwalk.KeyMapUpdater(...)). For example:

func TestBindings(t *testing.T) {
  m := New(...)
  catwalk.RunModel(t, "testdata/bindings", m, catwalk.WithUpdater(
    // The string "hello" is the prefix for identifying the keymap in tests.
	// Useful when the model contains multiple keymaps.
    catwalk.KeyMapUpdater("hello",
      func(m tea.Model, fn func(interface{}) error) (tea.Model, error) {
        tm := m.(YourModel)
        err := fn(&tm.KeyMap)
        return tm, err
    }),
  ))
}

After this, the input command keybind hello.X ... will automatically affect the binding .KeyMap.X in your model.

Alternatively, if your model implements tea.Model by reference (i.e. the address of its KeyMap does not change between Update calls), you can simplify as follows:

func TestBindings(t *testing.T) {
  m := New(...)
  catwalk.RunModel(t, "testdata/bindings", &m, catwalk.WithUpdater(
    // The string "hello" is the prefix for identifying the keymap in tests.
	// Useful when the model contains multiple keymaps.
    KeyMapUpdater("hello", catwalk.SimpleKeyMapApplier(&m.KeyMap))))
}

See the test TestRebind in bindings_test.go and the input file testdata/bindings for an example.

You can start using catwalk in your Bubbletea / Charm projects right away!

If you have any questions or comments:

• for bug fixes, feature requests, etc., file an issue
• for questions, suggestions, etc. you can come chat on the Charm Discord.