test: introduce basic tests for i/cmd/vermockgen

Prior to this change, there were no test files for the package:
github.com/Versent/go-vermock/internal/cmd/vermockgen.

This change introduces limited tests for SetFlags and Execute methods.

internal/cmd/vermockgen/gen_test.go

@@ -0,0 +1,36 @@
+package vermockgen_test
+
+import (
+	"bytes"
+	"flag"
+	"log"
+	"testing"
+
+	vermockgen "github.com/Versent/go-vermock/internal/cmd/vermockgen"
+)
+
+func TestSetFlags(t *testing.T) {
+	f := flag.NewFlagSet("vermockgen", flag.ContinueOnError)
+	vermockgen.NewGenCmd(nil, f)
+	expected := []string{"header", "tags"}
+	f.VisitAll(func(f *flag.Flag) {
+		if len(expected) == 0 {
+			t.Errorf("unexpected flag %q", f.Name)
+			return
+		}
+
+		var got, want string
+		got, want, expected = f.Name, expected[0], expected[1:]
+		if got != want {
+			t.Errorf("unexpected name, got %q, want %q", got, want)
+		}
+	})
+}
+
+func TestExecute(t *testing.T) {
+	var buf bytes.Buffer
+	l := log.New(&buf, "", 0)
+	f := flag.NewFlagSet("vermockgen", flag.ContinueOnError)
+	vermockgen.NewGenCmd(l, f)
+
+}