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[GH-ISSUE #326] Example for writing a test using a simulated tcell.Screen #248

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opened 2026-03-04 01:03:20 +03:00 by kerem · 1 comment
kerem commented 2026-03-04 01:03:20 +03:00
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Originally created by @Bios-Marcel on GitHub (Jul 23, 2019).
Original GitHub issue: https://github.com/rivo/tview/issues/326

I have been trying to write a test using tcell.SimulationScreen, but somehow I never reach a state where i can actually check the state. Instead it just times out after a while.

I have already tried manually invoking events on the tview.Application instance and the tcell.SimulationScreen, sadly that doesn't help either. I don't quite understand what's going on here. Am I missunderstanding something?

This is my testcode:

package ui

import (
	"fmt"
	"testing"

	"github.com/gdamore/tcell"
	"github.com/rivo/tview"
)

func TestExample(t *testing.T) {
	simScreen := tcell.NewSimulationScreen("UTF-8")
	simScreen.Init()
	simScreen.SetSize(10, 10)

	app := tview.NewApplication()
	app.SetScreen(simScreen)

	text := tview.NewTextView()
	text.SetText("C1")
	app.SetRoot(text, true)
	app.SetAfterDrawFunc(func(screen tcell.Screen) {
		fmt.Println("Afterdraw")
		cellOne, _, _, _ := simScreen.GetContent(0, 0)
		cellTwo, _, _, _ := simScreen.GetContent(0, 1)
		if cellOne != 'C' {
			t.Errorf("Cell missmatch. Was '%v' instead of '%v'.", cellOne, 'C')
		}
		if cellTwo != '4' {
			t.Errorf("Cell missmatch. Was '%v' instead of '%v'.", cellTwo, '4')
		}
	})
	app.SetBeforeDrawFunc(func(screen tcell.Screen) bool {
		fmt.Println("Beforedraw")
		return true
	})

	app.Run()
}

And this the result:

Running tool: /usr/local/go/bin/go test -timeout 30s github.com/Bios-Marcel/cordless/ui -run ^(TestExample)$

Beforedraw
panic: test timed out after 30s

goroutine 26 [running]:
testing.(*M).startAlarm.func1()
	/usr/local/go/src/testing/testing.go:1334 +0xdf
created by time.goFunc
	/usr/local/go/src/time/sleep.go:169 +0x44

goroutine 1 [chan receive]:
testing.(*T).Run(0xc00023ab00, 0xc0ae76, 0xb, 0xc81dc0, 0x480101)
	/usr/local/go/src/testing/testing.go:917 +0x381
testing.runTests.func1(0xc00023a900)
	/usr/local/go/src/testing/testing.go:1157 +0x78
testing.tRunner(0xc00023a900, 0xc0001ffe30)
	/usr/local/go/src/testing/testing.go:865 +0xc0
testing.runTests(0xc000152480, 0x12c4040, 0x3, 0x3, 0x0)
	/usr/local/go/src/testing/testing.go:1155 +0x2a9
testing.(*M).Run(0xc0004fdd00, 0x0)
	/usr/local/go/src/testing/testing.go:1072 +0x162
main.main()
	_testmain.go:46 +0x13e

goroutine 19 [syscall]:
os/signal.signal_recv(0x0)
	/usr/local/go/src/runtime/sigqueue.go:139 +0x9c
os/signal.loop()
	/usr/local/go/src/os/signal/signal_unix.go:23 +0x22
created by os/signal.init.0
	/usr/local/go/src/os/signal/signal_unix.go:29 +0x41

goroutine 7 [select]:
github.com/rivo/tview.(*Application).Run(0xc0004fdd80, 0x0, 0x0)
	/home/marcel/go/pkg/mod/github.com/rivo/tview@v0.0.0-20190721135419-23dc8a0944e4/application.go:204 +0x1bf
github.com/Bios-Marcel/cordless/ui.TestExample(0xc00023ab00)
	/home/marcel/code/cordless/ui/tview_test.go:38 +0x341
testing.tRunner(0xc00023ab00, 0xc81dc0)
	/usr/local/go/src/testing/testing.go:865 +0xc0
created by testing.(*T).Run
	/usr/local/go/src/testing/testing.go:916 +0x35a

goroutine 8 [select]:
github.com/gdamore/tcell.(*simscreen).PollEvent(0xc00055a2a0, 0xc82df0, 0xc0002abc90)
	/home/marcel/go/pkg/mod/github.com/gdamore/tcell@v1.1.4/simulation.go:346 +0xaf
github.com/rivo/tview.(*Application).Run.func2(0xc0002abc90, 0xc0004fdd80)
	/home/marcel/go/pkg/mod/github.com/rivo/tview@v0.0.0-20190721135419-23dc8a0944e4/application.go:173 +0xa0
created by github.com/rivo/tview.(*Application).Run
	/home/marcel/go/pkg/mod/github.com/rivo/tview@v0.0.0-20190721135419-23dc8a0944e4/application.go:160 +0x108
FAIL	github.com/Bios-Marcel/cordless/ui	30.016s
Error: Tests failed.
Originally created by @Bios-Marcel on GitHub (Jul 23, 2019). Original GitHub issue: https://github.com/rivo/tview/issues/326 I have been trying to write a test using tcell.SimulationScreen, but somehow I never reach a state where i can actually check the state. Instead it just times out after a while. I have already tried manually invoking events on the `tview.Application` instance and the `tcell.SimulationScreen`, sadly that doesn't help either. I don't quite understand what's going on here. Am I missunderstanding something? This is my testcode: ```go package ui import ( "fmt" "testing" "github.com/gdamore/tcell" "github.com/rivo/tview" ) func TestExample(t *testing.T) { simScreen := tcell.NewSimulationScreen("UTF-8") simScreen.Init() simScreen.SetSize(10, 10) app := tview.NewApplication() app.SetScreen(simScreen) text := tview.NewTextView() text.SetText("C1") app.SetRoot(text, true) app.SetAfterDrawFunc(func(screen tcell.Screen) { fmt.Println("Afterdraw") cellOne, _, _, _ := simScreen.GetContent(0, 0) cellTwo, _, _, _ := simScreen.GetContent(0, 1) if cellOne != 'C' { t.Errorf("Cell missmatch. Was '%v' instead of '%v'.", cellOne, 'C') } if cellTwo != '4' { t.Errorf("Cell missmatch. Was '%v' instead of '%v'.", cellTwo, '4') } }) app.SetBeforeDrawFunc(func(screen tcell.Screen) bool { fmt.Println("Beforedraw") return true }) app.Run() } ``` And this the result: ``` Running tool: /usr/local/go/bin/go test -timeout 30s github.com/Bios-Marcel/cordless/ui -run ^(TestExample)$ Beforedraw panic: test timed out after 30s goroutine 26 [running]: testing.(*M).startAlarm.func1() /usr/local/go/src/testing/testing.go:1334 +0xdf created by time.goFunc /usr/local/go/src/time/sleep.go:169 +0x44 goroutine 1 [chan receive]: testing.(*T).Run(0xc00023ab00, 0xc0ae76, 0xb, 0xc81dc0, 0x480101) /usr/local/go/src/testing/testing.go:917 +0x381 testing.runTests.func1(0xc00023a900) /usr/local/go/src/testing/testing.go:1157 +0x78 testing.tRunner(0xc00023a900, 0xc0001ffe30) /usr/local/go/src/testing/testing.go:865 +0xc0 testing.runTests(0xc000152480, 0x12c4040, 0x3, 0x3, 0x0) /usr/local/go/src/testing/testing.go:1155 +0x2a9 testing.(*M).Run(0xc0004fdd00, 0x0) /usr/local/go/src/testing/testing.go:1072 +0x162 main.main() _testmain.go:46 +0x13e goroutine 19 [syscall]: os/signal.signal_recv(0x0) /usr/local/go/src/runtime/sigqueue.go:139 +0x9c os/signal.loop() /usr/local/go/src/os/signal/signal_unix.go:23 +0x22 created by os/signal.init.0 /usr/local/go/src/os/signal/signal_unix.go:29 +0x41 goroutine 7 [select]: github.com/rivo/tview.(*Application).Run(0xc0004fdd80, 0x0, 0x0) /home/marcel/go/pkg/mod/github.com/rivo/tview@v0.0.0-20190721135419-23dc8a0944e4/application.go:204 +0x1bf github.com/Bios-Marcel/cordless/ui.TestExample(0xc00023ab00) /home/marcel/code/cordless/ui/tview_test.go:38 +0x341 testing.tRunner(0xc00023ab00, 0xc81dc0) /usr/local/go/src/testing/testing.go:865 +0xc0 created by testing.(*T).Run /usr/local/go/src/testing/testing.go:916 +0x35a goroutine 8 [select]: github.com/gdamore/tcell.(*simscreen).PollEvent(0xc00055a2a0, 0xc82df0, 0xc0002abc90) /home/marcel/go/pkg/mod/github.com/gdamore/tcell@v1.1.4/simulation.go:346 +0xaf github.com/rivo/tview.(*Application).Run.func2(0xc0002abc90, 0xc0004fdd80) /home/marcel/go/pkg/mod/github.com/rivo/tview@v0.0.0-20190721135419-23dc8a0944e4/application.go:173 +0xa0 created by github.com/rivo/tview.(*Application).Run /home/marcel/go/pkg/mod/github.com/rivo/tview@v0.0.0-20190721135419-23dc8a0944e4/application.go:160 +0x108 FAIL github.com/Bios-Marcel/cordless/ui 30.016s Error: Tests failed. ```
kerem closed this issue 2026-03-04 01:03:20 +03:00
kerem commented 2026-03-04 01:03:20 +03:00
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@Bios-Marcel commented on GitHub (Jul 24, 2019):

So, I was pretty much doing an integration test of the app. What I found out you can do instead, is to draw the actual components onto a tcell.SimulationScreen directly. Obviously you won't have the EventLoop logic and so on, but you don't really wanna test tview itself, so that should be fine.

<!-- gh-comment-id:514629390 --> @Bios-Marcel commented on GitHub (Jul 24, 2019): So, I was pretty much doing an integration test of the app. What I found out you can do instead, is to draw the actual components onto a `tcell.SimulationScreen` directly. Obviously you won't have the EventLoop logic and so on, but you don't really wanna test tview itself, so that should be fine.
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