NullPointerTester tester = new NullPointerTester();
tester.setDefault(StringBuilder.class, new StringBuilder());
// This is necessary because of the generics hackery we have to temporarily support parameters
// which implement both Iterator and Iterable.
tester.setDefault(Object.class, Iterators.emptyIterator());
tester.testAllPublicStaticMethods(Joiner.class);
tester.testAllPublicInstanceMethods(Joiner.on(","));
tester.testAllPublicInstanceMethods(Joiner.on(",").skipNulls());
tester.testAllPublicInstanceMethods(Joiner.on(",").useForNull("x"));
tester.testAllPublicInstanceMethods(
Joiner.on(",").withKeyValueSeparator("="));