diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 250ab1a..25fbbfd 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -21,3 +21,9 @@ jobs:
     - name: Build
       run: go build ./...
       working-directory: raylib
+    - name: Install gocovmerge
+      run: go install github.com/wadey/gocovmerge@latest
+      working-directory: .
+    - name: Coverage without view the results
+      run: go run coverage.go
+      working-directory: .
diff --git a/.gitignore b/.gitignore
index 824d669..70ddd37 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,5 @@
 
 # Ignore go.sum when go.mod is added.
 go.sum
+**/coverage_test.go
+**/*.coverage
diff --git a/coverage.go b/coverage.go
new file mode 100644
index 0000000..fdd6df1
--- /dev/null
+++ b/coverage.go
@@ -0,0 +1,200 @@
+package main
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+const (
+	exitName      = "exit_key"
+	coverage_test = `
+package main
+
+import (
+	"testing"
+	"time"
+)
+
+func Test(t *testing.T) {
+	go func() {
+		time.Sleep(time.Second)
+		exit_key = true
+	}()
+	main()
+}`
+)
+
+// coverage packages
+var coverpkgs = [...]string{
+	"github.com/gen2brain/raylib-go/raylib",
+	"github.com/gen2brain/raylib-go/raygui",
+}
+
+func main() {
+	// only for linux
+	switch runtime.GOOS {
+	case "linux", "darwin":
+		// do nothing
+	default:
+		log.Println("not supported OS")
+		return
+	}
+
+	view := flag.Bool("v", false, "view html result of coverage test")
+	flag.Parse()
+
+	// test of test
+	if !strings.Contains(coverage_test, exitName) {
+		log.Fatalln("source of main_test have not name: ", exitName)
+		return
+	}
+
+	// create templorary folder
+	tempDir, err := os.MkdirTemp("", "coverage")
+	if err != nil {
+		log.Fatal(err)
+		return
+	}
+	log.Println("Prepare test folder: ", tempDir)
+
+	// do not delete templorary folder
+	// defer os.Remove(tempDir.Name())
+
+	// 	// copy example folder
+	// 	log.Println("copy `examples` folder")
+	// 	if _, err := exec.Command("cp", "-r", "./examples/", tempDir).Output(); err != nil {
+	// 		log.Fatalf("%v", err)
+	// 		return
+	// 	}
+
+	// walking
+	log.Println("walking by temp folder with `main.go` files")
+	var testPaths []string
+	if err := filepath.Walk("./examples/",
+		func(path string, info os.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+			if !strings.HasSuffix(path, "main.go") {
+				return nil
+			}
+			index := strings.LastIndex(path, "/")
+			testPaths = append(testPaths, path[:index])
+			return nil
+		}); err != nil {
+		log.Fatalf("%v", err)
+		return
+	}
+
+	// TODO: create test in parallel
+	for index, testPath := range testPaths {
+		if 0 < flag.NArg() && !strings.Contains(testPath, os.Args[len(os.Args)-1]) {
+			continue
+		}
+		if err := coverage(index, testPath, tempDir); err != nil {
+			log.Fatalf("%v", err)
+			return
+		}
+	}
+
+	// combine coverage files
+	log.Println("combine coverage files")
+	var combineFiles []string
+	combineName := "all.coverage"
+	if err := filepath.Walk(tempDir,
+		func(path string, info os.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+			if info.IsDir() {
+				return nil
+			}
+			combineFiles = append(combineFiles, path)
+			fmt.Println(path)
+			return nil
+		}); err != nil {
+		log.Fatalf("%v", err)
+		return
+	}
+	cmd := exec.Command("gocovmerge", combineFiles...)
+	cmd.Dir = "./raygui/"
+	var out []byte
+	out, err = cmd.Output()
+	if err != nil {
+		log.Fatalf("gocovmerge: %v", err)
+		return
+	}
+	if err = os.WriteFile("./raygui/"+combineName, []byte(out), 0644); err != nil {
+		log.Fatalf("writefile: %v", err)
+		return
+	}
+
+	// run coverage
+	if *view {
+		log.Println("run coverage")
+		cmd = exec.Command(
+			"go", "tool", "cover",
+			"-html="+combineName,
+		)
+		cmd.Dir = "./raygui/"
+		if _, err = cmd.Output(); err != nil {
+			log.Fatalf("%v", err)
+			return
+		}
+	}
+}
+
+func coverage(index int, testPath, coverPath string) (err error) {
+	name := strings.ReplaceAll(testPath, coverPath, "")
+	log.Printf("run: %s", name)
+
+	// has file main.go
+	if _, err = os.Stat(testPath + "/main.go"); errors.Is(err, os.ErrNotExist) {
+		log.Printf("file `main.go` not exist")
+		return
+	}
+
+	// has exitName
+	{
+		var dat []byte
+		dat, err = os.ReadFile(testPath + "/main.go")
+		if err != nil {
+			log.Fatalf("readfile: %v", err)
+			return
+		}
+		if !strings.Contains(string(dat), exitName) {
+			log.Printf("file `main.go` have not `%s`", exitName)
+			return
+		}
+	}
+
+	// create main_test file
+	log.Println("create `main_test.go` file")
+	if err = os.WriteFile(testPath+"/coverage_test.go", []byte(coverage_test), 0644); err != nil {
+		log.Fatalf("writefile: %v", err)
+		return
+	}
+
+	// testing
+	log.Println("testing")
+	for ic, cpkg := range coverpkgs {
+		cmd := exec.Command(
+			"go", "test",
+			fmt.Sprintf("-coverprofile=%s/%d.%d.coverage", coverPath, index, ic),
+			fmt.Sprintf("-coverpkg=%s", cpkg),
+		)
+		cmd.Dir = testPath
+		if _, err = cmd.Output(); err != nil {
+			log.Fatalf("%v", err)
+			return
+		}
+	}
+	return
+}
diff --git a/examples/gui/basic_controls/main.go b/examples/gui/basic_controls/main.go
index b51838f..ff8fad8 100644
--- a/examples/gui/basic_controls/main.go
+++ b/examples/gui/basic_controls/main.go
@@ -8,6 +8,8 @@ import (
 	rl "github.com/gen2brain/raylib-go/raylib"
 )
 
+var exit_key = false
+
 func main() {
 	screenWidth := int32(800)
 	screenHeight := int32(450)
@@ -38,7 +40,7 @@ func main() {
 
 	rl.SetTargetFPS(60)
 
-	for !rl.WindowShouldClose() {
+	for !(rl.WindowShouldClose() || exit_key) {
 		if buttonClicked {
 			progressValue += 0.1
 			if progressValue >= 1.1 {
diff --git a/examples/gui/button/go.mod b/examples/gui/button/go.mod
index 7ce5cb7..2d205c1 100644
--- a/examples/gui/button/go.mod
+++ b/examples/gui/button/go.mod
@@ -6,3 +6,6 @@ require (
 	github.com/gen2brain/raylib-go/raygui v0.0.0-20221117130019-ce3c8e83dd6d
 	github.com/gen2brain/raylib-go/raylib v0.0.0-20221117130019-ce3c8e83dd6d
 )
+
+replace github.com/gen2brain/raylib-go/raylib => ../../../raylib
+replace github.com/gen2brain/raylib-go/raygui => ../../../raygui
diff --git a/examples/gui/button/main.go b/examples/gui/button/main.go
index c7b3a12..0823295 100644
--- a/examples/gui/button/main.go
+++ b/examples/gui/button/main.go
@@ -3,10 +3,12 @@ package main
 import (
 	"fmt"
 
-	rl  "github.com/gen2brain/raylib-go/raylib"
-	gui  "github.com/gen2brain/raylib-go/raygui"
+	gui "github.com/gen2brain/raylib-go/raygui"
+	rl "github.com/gen2brain/raylib-go/raylib"
 )
 
+var exit_key = false
+
 func main() {
 	rl.InitWindow(800, 450, "raygui - button")
 
@@ -14,7 +16,7 @@ func main() {
 
 	var button bool
 
-	for !rl.WindowShouldClose() {
+	for !(rl.WindowShouldClose() || exit_key) {
 		rl.BeginDrawing()
 
 		rl.ClearBackground(rl.Black)
diff --git a/examples/gui/controls_test_suite/controls_test_suite.go b/examples/gui/controls_test_suite/main.go
similarity index 98%
rename from examples/gui/controls_test_suite/controls_test_suite.go
rename to examples/gui/controls_test_suite/main.go
index 1cad647..80d2a60 100644
--- a/examples/gui/controls_test_suite/controls_test_suite.go
+++ b/examples/gui/controls_test_suite/main.go
@@ -7,6 +7,8 @@ import (
 	rl "github.com/gen2brain/raylib-go/raylib"
 )
 
+var exit_key = false
+
 /*******************************************************************************************
 *
 *   raygui - controls test suite
@@ -123,7 +125,7 @@ func main() {
 	//--------------------------------------------------------------------------------------
 
 	// Main game loop
-	for !exitWindow { // Detect window close button or ESC key
+	for !(exitWindow || exit_key) { // Detect window close button or ESC key
 		// Update
 		//----------------------------------------------------------------------------------
 		exitWindow = rl.WindowShouldClose()
@@ -228,7 +230,7 @@ func main() {
 		sliderValue = gui.Slider(rl.Rectangle{355, 400, 165, 20}, "TEST",
 			fmt.Sprintf("%2.2f", sliderValue), sliderValue, -50, 100)
 		sliderBarValue = gui.SliderBar(rl.Rectangle{320, 430, 200, 20}, "",
-			fmt.Sprint("%d", sliderBarValue), sliderBarValue, 0, 100)
+			fmt.Sprintf("%2.2f", sliderBarValue), sliderBarValue, 0, 100)
 		progressValue = gui.ProgressBar(rl.Rectangle{320, 460, 200, 20}, "", "", progressValue, 0, 1)
 
 		// NOTE: View rectangle could be used to perform some scissor test
diff --git a/examples/gui/portable_window/portable_window.go b/examples/gui/portable_window/main.go
similarity index 96%
rename from examples/gui/portable_window/portable_window.go
rename to examples/gui/portable_window/main.go
index 2e4754b..aaa8efd 100644
--- a/examples/gui/portable_window/portable_window.go
+++ b/examples/gui/portable_window/main.go
@@ -24,6 +24,8 @@ import (
 *
 **********************************************************************************************/
 
+var exit_key = false
+
 //------------------------------------------------------------------------------------
 // Program main entry point
 //------------------------------------------------------------------------------------
@@ -54,7 +56,7 @@ func main() {
 	//--------------------------------------------------------------------------------------
 
 	// Main game loop
-	for !exitWindow && !rl.WindowShouldClose() { // Detect window close button or ESC key
+	for !(exitWindow || rl.WindowShouldClose() || exit_key) { // Detect window close button or ESC key
 		// Update
 		//----------------------------------------------------------------------------------
 		mousePosition = rl.GetMousePosition()
diff --git a/examples/gui/scroll_panel/scroll_panel.go b/examples/gui/scroll_panel/main.go
similarity index 92%
rename from examples/gui/scroll_panel/scroll_panel.go
rename to examples/gui/scroll_panel/main.go
index dc6e207..2fbf478 100644
--- a/examples/gui/scroll_panel/scroll_panel.go
+++ b/examples/gui/scroll_panel/main.go
@@ -30,6 +30,8 @@ import (
 *
 **********************************************************************************************/
 
+var exit_key = false
+
 //------------------------------------------------------------------------------------
 // Program main entry point
 //------------------------------------------------------------------------------------
@@ -56,7 +58,7 @@ func main() {
 	//---------------------------------------------------------------------------------------
 
 	// Main game loop
-	for !rl.WindowShouldClose() {
+	for !(rl.WindowShouldClose() || exit_key) {
 		// Detect window close button or ESC key
 
 		// Update
@@ -85,10 +87,10 @@ func main() {
 
 		if showContentArea {
 			rl.DrawRectangle(
-			int32(panelRec.X+panelScroll.X),
-			int32(panelRec.Y+panelScroll.Y),
-			int32(panelContentRec.Width),
-			int32(panelContentRec.Height),
+				int32(panelRec.X+panelScroll.X),
+				int32(panelRec.Y+panelScroll.Y),
+				int32(panelContentRec.Width),
+				int32(panelContentRec.Height),
 				rl.Fade(rl.Red, 0.1),
 			)
 		}
@@ -140,7 +142,7 @@ func DrawStyleEditControls() {
 	gui.Spinner(rl.Rectangle{670, 240, 90, 20}, "", &style, 0, 14, false)
 	gui.SetStyle(gui.SCROLLBAR, gui.SLIDER_PADDING, style)
 
-	style = boolToint32( gui.CheckBox(rl.Rectangle{565, 280, 20, 20}, "ARROWS_VISIBLE", int32Tobool(gui.GetStyle(gui.SCROLLBAR, gui.ARROWS_VISIBLE))))
+	style = boolToint32(gui.CheckBox(rl.Rectangle{565, 280, 20, 20}, "ARROWS_VISIBLE", int32Tobool(gui.GetStyle(gui.SCROLLBAR, gui.ARROWS_VISIBLE))))
 	gui.SetStyle(gui.SCROLLBAR, gui.ARROWS_VISIBLE, style)
 
 	style = gui.GetStyle(gui.SCROLLBAR, gui.SLIDER_PADDING)
@@ -159,7 +161,7 @@ func DrawStyleEditControls() {
 	} else {
 		text = "SCROLLBAR: RIGHT"
 	}
-	style = boolToint32( gui.Toggle(rl.Rectangle{560, 110, 200, 35}, text, int32Tobool(gui.GetStyle(gui.LISTVIEW, gui.SCROLLBAR_SIDE))))
+	style = boolToint32(gui.Toggle(rl.Rectangle{560, 110, 200, 35}, text, int32Tobool(gui.GetStyle(gui.LISTVIEW, gui.SCROLLBAR_SIDE))))
 	gui.SetStyle(gui.LISTVIEW, gui.SCROLLBAR_SIDE, style)
 	//----------------------------------------------------------
 
diff --git a/raygui/go.mod b/raygui/go.mod
index c2adde5..3822e0b 100644
--- a/raygui/go.mod
+++ b/raygui/go.mod
@@ -4,4 +4,4 @@ go 1.19
 
 require github.com/gen2brain/raylib-go/raylib v0.0.0-20221117130019-ce3c8e83dd6d
 
-replace github.com/gen2brain/raylib-go/raylib => ../../../raylib
+replace github.com/gen2brain/raylib-go/raylib => ../raylib