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# Testing
## Overview
go-tui ships with `MockTerminal` and `MockEventReader` so you can test components without a real terminal. `MockTerminal` captures rendered output into an in-memory cell buffer you can inspect. `MockEventReader` queues up keyboard and mouse events and replays them on demand. Between them, you can render elements, simulate input, and assert on visual output and state changes from plain `go test`.
## MockTerminal
`MockTerminal` implements the `Terminal` interface. It maintains an internal grid of cells that records every write operation, so you can verify what your UI looks like after rendering.
Create one with a width and height (in characters and rows):
```go
term := tui.NewMockTerminal(80, 24)
```
### Reading Output
The two most common assertions use `String()` and `StringTrimmed()`:
```go
// Full buffer as a string (rows joined by newlines)
output := term.String()
// Same, but trailing spaces stripped from each line
output := term.StringTrimmed()
```
For cell-level checks, use `CellAt(x, y)`:
```go
cell := term.CellAt(5, 2)
if cell.Rune != 'H' {
t.Errorf("CellAt(5, 2) = %q, want 'H'", cell.Rune)
}
// Check styling too
if !cell.Style.HasAttr(tui.AttrBold) {
t.Error("expected bold text")
}
if !cell.Style.Fg.Equal(tui.Red) {
t.Error("expected red foreground")
}
```
### Checking Terminal State
`MockTerminal` tracks mode switches so you can verify your app entered the right states:
```go
term.IsInRawMode() // true after EnterRawMode()
term.IsInAltScreen() // true after EnterAltScreen()
term.IsMouseEnabled() // true after EnableMouse()
term.IsCursorHidden() // true after HideCursor()
```
It also counts alternate screen transitions:
```go
term.AltScreenEnterCount() // how many times EnterAltScreen was called
term.AltScreenExitCount() // how many times ExitAltScreen was called
```
### Resizing and Resetting
Resize the mock terminal to test layout changes:
```go
term.Resize(120, 40)
```
Reset clears the entire buffer and all state flags back to initial values:
```go
term.Reset()
```
You can also set terminal capabilities to test color degradation:
```go
term.SetCaps(tui.Capabilities{
Colors: tui.Color256,
TrueColor: false,
Unicode: true,
AltScreen: true,
})
```
## MockEventReader
`MockEventReader` implements `EventReader` and `InterruptibleReader`. It holds a queue of events and returns them one at a time through `PollEvent`.
Create one with events pre-loaded:
```go
reader := tui.NewMockEventReader(
tui.KeyEvent{Key: tui.KeyRune, Rune: 'h'},
tui.KeyEvent{Key: tui.KeyRune, Rune: 'i'},
tui.KeyEvent{Key: tui.KeyEnter},
)
```
Pull events out with `PollEvent`. When the queue is empty, it returns `(nil, false)`:
```go
event, ok := reader.PollEvent(0)
if !ok {
// no more events
}
```
Add more events after creation:
```go
reader.AddEvents(
tui.KeyEvent{Key: tui.KeyEscape},
)
```
Check how many events are left:
```go
remaining := reader.Remaining()
```
Reset the reader to replay from the beginning:
```go
reader.Reset()
```
## Testing Rendered Output
The simplest test renders an element tree to a buffer and checks the result. No app setup needed.
```go
func TestPanel_RendersBorder(t *testing.T) {
// Build the element tree
root := tui.New(
tui.WithSize(80, 24),
tui.WithDirection(tui.Column),
)
panel := tui.New(
tui.WithSize(20, 5),
tui.WithBorder(tui.BorderSingle),
)
root.AddChild(panel)
// Render to a buffer
buf := tui.NewBuffer(80, 24)
root.Render(buf, 80, 24)
// Check the panel got the right dimensions
rect := panel.Rect()
if rect.Width != 20 || rect.Height != 5 {
t.Errorf("panel size = %dx%d, want 20x5", rect.Width, rect.Height)
}
// Verify the top-left corner of the single border
cell := buf.Cell(rect.X, rect.Y)
if cell.Rune != '┌' {
t.Errorf("top-left = %q, want '┌'", cell.Rune)
}
}
```
For snapshot-style tests, render to a `MockTerminal` and check `StringTrimmed()`:
```go
func TestGreeting_ShowsMessage(t *testing.T) {
buf := tui.NewBuffer(30, 5)
term := tui.NewMockTerminal(30, 5)
style := tui.NewStyle()
buf.SetString(2, 1, "Hello, World!", style)
tui.Render(term, buf)
output := term.StringTrimmed()
if !strings.Contains(output, "Hello, World!") {
t.Errorf("expected 'Hello, World!' in output:\n%s", output)
}
}
```
### Verifying Styled Output
You can check that cells carry the right styles by inspecting individual cell attributes:
```go
func TestStyledBox(t *testing.T) {
buf := tui.NewBuffer(25, 7)
term := tui.NewMockTerminal(25, 7)
// Draw a rounded box with blue border
boxStyle := tui.NewStyle().Foreground(tui.Blue)
tui.DrawBox(buf, tui.NewRect(1, 1, 20, 5), tui.BorderRounded, boxStyle)
// Draw bold red text inside
textStyle := tui.NewStyle().Bold().Foreground(tui.Red)
buf.SetString(3, 3, "Alert!", textStyle)
tui.Render(term, buf)
// Verify border style
corner := term.CellAt(1, 1)
if corner.Rune != '╭' {
t.Errorf("top-left = %q, want '╭'", corner.Rune)
}
if !corner.Style.Fg.Equal(tui.Blue) {
t.Error("border should be blue")
}
// Verify text style
cell := term.CellAt(3, 3)
if !cell.Style.HasAttr(tui.AttrBold) {
t.Error("text should be bold")
}
}
```
## Testing Key Handling
To test that a component's `KeyMap` responds correctly, build the component, call `KeyMap()`, and check the returned bindings against specific events. Here's a pattern that tests state changes after key presses:
```go
func TestCounter_KeyMap(t *testing.T) {
type tc struct {
key tui.KeyEvent
wantCount int
}
tests := map[string]tc{
"increment with +": {
key: tui.KeyEvent{Key: tui.KeyRune, Rune: '+'},
wantCount: 1,
},
"decrement with -": {
key: tui.KeyEvent{Key: tui.KeyRune, Rune: '-'},
wantCount: -1,
},
}
for name, tt := range tests {
t.Run(name, func(t *testing.T) {
c := NewCounter() // your component constructor
km := c.KeyMap()
// Find the matching binding and call its handler
for _, binding := range km {
if binding.Pattern.AnyRune && tt.key.IsRune() {
binding.Handler(tt.key)
break
}
if binding.Pattern.Rune == tt.key.Rune && tt.key.IsRune() {
binding.Handler(tt.key)
break
}
if binding.Pattern.Key == tt.key.Key && !tt.key.IsRune() {
binding.Handler(tt.key)
break
}
}
if c.count.Get() != tt.wantCount {
t.Errorf("count = %d, want %d", c.count.Get(), tt.wantCount)
}
})
}
}
```
### Testing with FocusManager
For more realistic input testing, wire up a `FocusManager` with a `MockEventReader`. The `FocusManager` routes events to whatever element has focus, so you can test the full input pipeline.
You'll need a type that implements the `Focusable` interface (`IsFocusable`, `HandleEvent`, `Focus`, `Blur`). Here's a minimal test helper:
```go
type testFocusable struct {
focused bool
lastEvent tui.Event
handled bool
}
func (f *testFocusable) IsFocusable() bool { return true }
func (f *testFocusable) Focus() { f.focused = true }
func (f *testFocusable) Blur() { f.focused = false }
func (f *testFocusable) HandleEvent(e tui.Event) bool { f.lastEvent = e; return f.handled }
```
Then use it in a test:
```go
func TestInput_ReceivesEvents(t *testing.T) {
events := []tui.Event{
tui.KeyEvent{Key: tui.KeyRune, Rune: 'h'},
tui.KeyEvent{Key: tui.KeyRune, Rune: 'i'},
tui.KeyEvent{Key: tui.KeyEnter},
}
reader := tui.NewMockEventReader(events...)
elem := &testFocusable{handled: true}
fm := tui.NewFocusManager()
fm.Register(elem)
// Process all events
for {
event, ok := reader.PollEvent(0)
if !ok {
break
}
fm.Dispatch(event)
}
// Last event should be Enter
last := elem.lastEvent.(tui.KeyEvent)
if last.Key != tui.KeyEnter {
t.Errorf("last event = %v, want KeyEnter", last.Key)
}
}
```
## Testing Resize Behavior
Test that your layout adapts to terminal size changes by rendering at different dimensions:
```go
func TestLayout_AdaptsToResize(t *testing.T) {
type tc struct {
width int
height int
wantPanelW int
}
tests := map[string]tc{
"narrow terminal": {
width: 40,
height: 24,
wantPanelW: 40,
},
"wide terminal": {
width: 120,
height: 24,
wantPanelW: 120,
},
}
for name, tt := range tests {
t.Run(name, func(t *testing.T) {
root := tui.New(
tui.WithDirection(tui.Column),
)
panel := tui.New(
tui.WithFlexGrow(1),
tui.WithHeight(10),
)
root.AddChild(panel)
buf := tui.NewBuffer(tt.width, tt.height)
root.Render(buf, tt.width, tt.height)
rect := panel.Rect()
if rect.Width != tt.wantPanelW {
t.Errorf("panel width = %d, want %d", rect.Width, tt.wantPanelW)
}
})
}
}
```
## Table-Driven Tests
go-tui uses table-driven tests throughout. Define the `tc` struct before the test map, use `map[string]tc` for named cases, and iterate with `t.Run`:
```go
func TestMyComponent(t *testing.T) {
type tc struct {
initialCount int
keyPresses []rune
wantCount int
}
tests := map[string]tc{
"no keys pressed": {
initialCount: 0,
keyPresses: nil,
wantCount: 0,
},
"three increments": {
initialCount: 0,
keyPresses: []rune{'+', '+', '+'},
wantCount: 3,
},
"increment then decrement": {
initialCount: 5,
keyPresses: []rune{'+', '-'},
wantCount: 5,
},
}
for name, tt := range tests {
t.Run(name, func(t *testing.T) {
c := NewCounter()
c.count.Set(tt.initialCount)
km := c.KeyMap()
for _, r := range tt.keyPresses {
event := tui.KeyEvent{Key: tui.KeyRune, Rune: r}
for _, binding := range km {
if binding.Pattern.Rune == r {
binding.Handler(event)
break
}
}
}
if c.count.Get() != tt.wantCount {
t.Errorf("count = %d, want %d", c.count.Get(), tt.wantCount)
}
})
}
}
```
The `tc` struct lives inside the test function. Each test case has a descriptive name that shows up in `go test -v` output. The pattern keeps individual test functions short and makes it simple to add new cases.
## Tips
**Test rendering and behavior separately.** Rendering tests verify layout and visual output. Behavior tests verify state changes from key events. Mixing them makes failures harder to diagnose.
**Use `StringTrimmed()` over `String()`.** `String()` preserves trailing spaces on every line, which makes string comparisons brittle. `StringTrimmed()` strips trailing whitespace, giving you cleaner snapshot comparisons.
**Check cells, not full strings, for precise assertions.** `CellAt(x, y)` lets you verify a specific character and its style without worrying about surrounding whitespace. Use `strings.Contains` on `StringTrimmed()` for coarser checks.
**Keep your MockTerminal the same size as your Buffer.** If they differ, the render may clip or produce unexpected results.
## Next Steps
- [Multi-Component Applications](multi-component) -- Building apps with multiple struct components and shared state
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