Fix up structure for better testing

pkg/browser/browser.go

@@ -52,15 +52,18 @@ func FromLauncher(launcher, url string) (*exec.Cmd, error) {
 	return cmd, nil
 }
 
-var linuxExe = func() string {
+func linuxExe() string {
 	exe := "xdg-open"
-	if !findExe("xdg-open") && findExe("wslview") {
-		exe = "wslview"
+
+	_, err := lookPath(exe)
+	if err != nil {
+		_, err := lookPath("wslview")
+		if err == nil {
+			exe = "wslview"
+		}
 	}
+
 	return exe
 }
 
-func findExe(command string) bool {
-	_, err := exec.LookPath(command)
-	return err == nil
-}
+var lookPath = exec.LookPath

pkg/browser/browser_test.go

@@ -1,6 +1,7 @@
 package browser
 
 import (
+	"errors"
 	"reflect"
 	"testing"
 )
@@ -52,8 +53,15 @@ func TestForOS(t *testing.T) {
 		},
 	}
 	for _, tt := range tests {
+		lookPath = func(file string) (string, error) {
+			if file == tt.exe {
+				return file, nil
+			} else {
+				return "", errors.New("not found")
+			}
+		}
+
 		t.Run(tt.name, func(t *testing.T) {
-			linuxExe = func() string { return tt.exe }
 			if cmd := ForOS(tt.args.goos, tt.args.url); !reflect.DeepEqual(cmd.Args, tt.want) {
 				t.Errorf("ForOS() = %v, want %v", cmd.Args, tt.want)
 			}