Really fix TestApp_RunAsSubCommandIncorrectUsage

An earlier commit 6564c0f made an attempt at fixing this test,
but apparently it is not working correctly with Go <= 1.16, because
the panic is expected, and it only happens with Go 1.17+.

Rather than adding an ugly kludge checking the runtime go version,
let's have two versions of the test.

Once Go 1.16 is no longer supported, we can remove the go116_test.go
file.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

app_test.go

@@ -507,31 +507,6 @@ func TestApp_RunAsSubcommandParseFlags(t *testing.T) {
 	expect(t, context.String("lang"), "spanish")
 }
 
-func TestApp_RunAsSubCommandIncorrectUsage(t *testing.T) {
-	// Go 1.17+ panics when invalid flag is given.
-	// Catch it here and consider the test passed.
-	defer func() {
-		if err := recover(); err == nil {
-			t.Fatal("expected error, got nothing")
-		}
-	}()
-
-	a := App{
-		Flags: []Flag{
-			StringFlag{Name: "--foo"},
-		},
-		Writer: bytes.NewBufferString(""),
-	}
-
-	set := flag.NewFlagSet("", flag.ContinueOnError)
-	_ = set.Parse([]string{"", "---foo"})
-	c := &Context{flagSet: set}
-
-	err := a.RunAsSubcommand(c)
-
-	expect(t, err, errors.New("bad flag syntax: ---foo"))
-}
-
 func TestApp_CommandWithFlagBeforeTerminator(t *testing.T) {
 	var parsedOption string
 	var args []string

go116_test.go

@@ -0,0 +1,28 @@
+//go:build !go1.17
+// +build !go1.17
+
+package cli
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"testing"
+)
+
+func TestApp_RunAsSubCommandIncorrectUsage(t *testing.T) {
+	a := App{
+		Flags: []Flag{
+			StringFlag{Name: "--foo"},
+		},
+		Writer: bytes.NewBufferString(""),
+	}
+
+	set := flag.NewFlagSet("", flag.ContinueOnError)
+	_ = set.Parse([]string{"", "---foo"})
+	c := &Context{flagSet: set}
+
+	err := a.RunAsSubcommand(c)
+
+	expect(t, err, errors.New("bad flag syntax: ---foo"))
+}

go117_test.go

@@ -0,0 +1,33 @@
+//go:build go1.17
+// +build go1.17
+
+package cli
+
+import (
+	"bytes"
+	"flag"
+	"testing"
+)
+
+func TestApp_RunAsSubCommandIncorrectUsage(t *testing.T) {
+	a := App{
+		Flags: []Flag{
+			StringFlag{Name: "--foo"},
+		},
+		Writer: bytes.NewBufferString(""),
+	}
+
+	set := flag.NewFlagSet("", flag.ContinueOnError)
+	_ = set.Parse([]string{"", "---foo"})
+	c := &Context{flagSet: set}
+
+	// Go 1.17+ panics when invalid flag is given.
+	// Catch it here and consider the test passed.
+	defer func() {
+		if err := recover(); err == nil {
+			t.Fatal("expected error, got nothing")
+		}
+	}()
+
+	_ = a.RunAsSubcommand(c)
+}