Cleanup ostream interface

test/ostream-test.cc

@@ -258,7 +258,8 @@ std::ostream& operator<<(std::ostream& os, streamable_and_convertible_to_bool) {
 }
 
 TEST(ostream_test, format_convertible_to_bool) {
-  EXPECT_EQ("foo", fmt::format("{}", streamable_and_convertible_to_bool()));
+  // operator<< is intentionally not used because of potential ODR violations.
+  EXPECT_EQ(fmt::format("{}", streamable_and_convertible_to_bool()), "true");
 }
 
 struct copyfmt_test {};