1 files changed, 60 insertions, 0 deletions
diff --git a/src/flag/flag_test.go b/src/flag/flag_test.go
index 8c88c8c27..80d92a5e7 100644
--- a/src/flag/flag_test.go
+++ b/src/flag/flag_test.go
@@ -377,3 +377,63 @@ func TestHelp(t *testing.T) {
 		t.Fatal("help was called; should not have been for defined help flag")
 	}
 }
+
+// Test that a standard flag can be set only once. Need to verify every flag type.
+// User-defined flags can be set multiple times, and this is verified in the tests above.
+func TestErrorOnMultipleSettings(t *testing.T) {
+	check := func(typ string, err error) {
+		if err == nil {
+			t.Errorf("%s flag can be set multiple times")
+		} else if !strings.Contains(err.Error(), "flag set multiple") {
+			t.Fatalf("expected multiple setting error, got %q", err)
+		}
+	}
+	{
+		var flags FlagSet
+		flags.Init("test", ContinueOnError)
+		flags.Bool("v", false, "usage")
+		check("bool", flags.Parse([]string{"-v", "-v"}))
+	}
+	{
+		var flags FlagSet
+		flags.Init("test", ContinueOnError)
+		flags.Int("v", 0, "usage")
+		check("int", flags.Parse([]string{"-v", "1", "-v", "2"}))
+	}
+	{
+		var flags FlagSet
+		flags.Init("test", ContinueOnError)
+		flags.Int64("v", 0, "usage")
+		check("int64", flags.Parse([]string{"-v", "1", "-v", "2"}))
+	}
+	{
+		var flags FlagSet
+		flags.Init("test", ContinueOnError)
+		flags.Uint("v", 0, "usage")
+		check("uint", flags.Parse([]string{"-v", "1", "-v", "2"}))
+	}
+	{
+		var flags FlagSet
+		flags.Init("test", ContinueOnError)
+		flags.Uint64("v", 0, "usage")
+		check("uint64", flags.Parse([]string{"-v", "1", "-v", "2"}))
+	}
+	{
+		var flags FlagSet
+		flags.Init("test", ContinueOnError)
+		flags.String("v", "", "usage")
+		check("string", flags.Parse([]string{"-v", "1", "-v", "2"}))
+	}
+	{
+		var flags FlagSet
+		flags.Init("test", ContinueOnError)
+		flags.Float64("v", 0, "usage")
+		check("float64", flags.Parse([]string{"-v", "1", "-v", "2"}))
+	}
+	{
+		var flags FlagSet
+		flags.Init("test", ContinueOnError)
+		flags.Duration("v", 0, "usage")
+		check("duration", flags.Parse([]string{"-v", "1s", "-v", "2s"}))
+	}
+}