src/main/java/org/fest/assertions/error/ShouldContainStringOnlyOnce.java
public static ErrorMessageFactory shouldContainOnlyOnce(String actual, String sequence, int occurences) {
    return new ShouldContainStringOnlyOnce(actual, sequence, occurences);
  }
public static ErrorMessageFactory shouldContainOnlyOnce(String actual, String sequence, int occurences) {
    return new ShouldContainStringOnlyOnce(actual, sequence, occurences);
  }
Creates a new <code>{@link ShouldContainStringOnlyOnce}</code>.

@param actual the actual value in the failed assertion.
@param sequence the String expected to be in {@code actual} only once.
@param occurences the number of occurrences of sequence in actual.
@return the created {@code ErrorMessageFactory}.