### Question:
SimpleStringUtils { public static boolean equals(String str1, String str2) { if (str1 == null && str2 == null) { return true; } if (str1 == null || str2 == null) { return false; } return str1.equals(str2); } private  SimpleStringUtils(); static boolean equals(String str1, String str2); static boolean startsWith(String part, String full); static String emptyToNull(String value); static String truncateWhenTooLong(String string, int maxLength);  }### Answer:
@Test public void null_equals_null_returns_true() { assertThat(SimpleStringUtils.equals(null, null), is(true)); }
@Test public void null_equals_not_empty_strings_returns_false() { assertThat(SimpleStringUtils.equals(null, "string"), is(false)); assertThat(SimpleStringUtils.equals(null, ""), is(false)); assertThat(SimpleStringUtils.equals("",null), is(false)); assertThat(SimpleStringUtils.equals("string",null), is(false)); }
@Test public void string1_equals_string2_returns_false() { assertThat(SimpleStringUtils.equals("string1", "string2"), is(false)); }
@Test public void same_strings_equals_returns_true() { assertThat(SimpleStringUtils.equals("string1", "string1"), is(true)); assertThat(SimpleStringUtils.equals("", ""), is(true)); }