Lab 6: JUnit Testing

Overview

Having thorough tests can ensure the behavior of a class matches its specification, but writing thorough tests can be challenging. In this assignment you will gain experience writing unit tests for an AutoCompleter interface and use it to test your own implementation of the interface.

Assignment

AutoCompleter interface

The AutoCompleter interface has the following methods:

• boolean add(String word) — returns true if word is added to the object (a word should not be added if it is already in the auto completer). If word is null or an empty string, an IllegalArgumentException is thrown.
• int size() — returns the number of items in the auto completer.
• boolean exactMatch(String target) — returns true if target is found in the auto completer. If target is null or an empty string, the method returns false.
• String[] allMatches(String prefix) — returns an array of all the strings in the object that begin with the prefix. If prefix is an empty string, an array of all the strings in the auto completer are returned. If prefix is null, an empty array is returned.
• String getBackingClass() — returns a String indicating the fully qualified name of the data structure used to store the words for the AutoCompleter. E.g., "java.util.ArrayList".
• static String format(long nanoseconds) — returns a human-friendly string representing the number of nanoseconds. The format of the string must be consistent with the examples and rules below. Note: this method is declared static which means that it should be implemented in the interface. If a negative value is supplied, the method should throw an IllegalArgumentException.

All words stored by an AutoCompleter implementation for this assignment should be converted to lowercase. As a result, duplicate detection, exact matching, and prefix matching are case-insensitive. For example, "Dog", "DOG", and "dog" represent the same stored word, and a prefix of "Al" should match a stored word such as "alpha".

The format() method should select the largest time unit for which the first displayed value is at least 1. Use the following output forms:

Examples include:

• 2 days 5 hours 32 minutes
• 14 hours 1 minute 8 seconds
• 42 minutes 55.3 seconds
• 18.8 seconds
• 998.8 milliseconds
• 318.8 microseconds
• 7 nanoseconds
• 0 nanoseconds

Values should remain in the unit selected by the original nanosecond value, even if rounding causes the displayed value to reach the next unit. For example, 999_999 nanoseconds should be displayed as 1000.0 microseconds, not 1.0 millisecond.

You must implement the static format() method and write complete javadocs for all the methods in AutoCompleter.

Unordered List Implementation

You must create a class, UnorderedList, that implements the AutoCompleter interface using an unordered list. Your class must have only one private attribute: private final List<String> items that is assigned via a one-argument constructor.

The constructor must:

• throw an IllegalArgumentException if the supplied List is null,
• use the supplied List object as the backing data structure rather than creating a different list,
• convert the supplied words to lowercase,
• remove duplicate words while preserving the order of their first occurrence.

You may assume that the List passed to the constructor is modifiable and does not contain null elements.

List<String> unique = items.stream().distinct().toList();
items.clear();
items.addAll(unique);

Testing

You must create JUnit tests for all of the methods in the AutoCompleter interface. These tests should be rigorous and ensure all methods behave as specified in the requirements. If the behavior of specific methods is not completely specified, please ask your instructor for clarification.

Your tests should consider normal cases, boundary cases, invalid input, and behavior that may change as data is added to the auto completer. A test suite that demonstrates only that a correct implementation works is not necessarily thorough; your tests should also be capable of distinguishing correct behavior from plausible incorrect implementations.

Use the tests to ensure your UnorderedList implementation conforms to the requirements.

Your instructor may verify your tests by providing multiple faulty implementations to see if your tests catch the errors embedded in the faulty implementations.

Acknowledgement

This laboratory assignment, developed by Dr. Chris Taylor.