### Question:
SystemPropertyListBuilder { public String build(String type, String key, String value){ StringBuilder sb = new StringBuilder(); sb.append("-D"); sb.append(type); sb.append('.'); sb.append(key); sb.append('='); sb.append(value); return sb.toString(); }  String build(String type, String key, String value);  }### Answer:
@Test public void prefix_key_value_returned_as_system_property_entry() { assertEquals("-Dprefix.key=value",builderToTest.build("prefix", "key", "value")); }
@Test public void null_key_value_returned_as_system_property_entry() { assertEquals("-Dnull.key=value",builderToTest.build(null, "key", "value")); }
@Test public void prefix_null_value_returned_as_system_property_entry() { assertEquals("-Dprefix.null=value",builderToTest.build("prefix", null, "value")); }
@Test public void prefix_key_null_returned_as_system_property_entry() { assertEquals("-Dprefix.key=null",builderToTest.build("prefix", "key",null)); }