src/main/java/org/fest/assertions/internal/Collections.java
public void assertDoesNotHaveDuplicates(Description description, Collection<?> actual) {
    assertNotNull(description, actual);
    Collection<?> duplicates = duplicatesFrom(actual);
    if (duplicates.isEmpty()) {
      return;
    }
    throw failures.failure(description, shouldNotHaveDuplicates(actual, duplicates));
  }
public void assertDoesNotHaveDuplicates(Description description, Collection<?> actual) {
    assertNotNull(description, actual);
    Collection<?> duplicates = duplicatesFrom(actual);
    if (duplicates.isEmpty()) {
      return;
    }
    throw failures.failure(description, shouldNotHaveDuplicates(actual, duplicates));
  }
Asserts that the given {@code Collection} does not have duplicate values.

@param description contains information about the assertion.
@param actual      the given {@code Collection}.
@throws NullPointerException     if the array of values is {@code null}.
@throws IllegalArgumentException if the array of values is empty.
@throws AssertionError           if the given {@code Collection} is {@code null}.
@throws AssertionError           if the given {@code Collection} contains duplicate values.