Required methods

You should have an "is-Method" for each nonterminal defined in the grammar. Specifically,

isAction isAddOperator isAllbugsCode isArithmeticExpression isAssignmentStatement isBlock isBugDefinition isColorStatement isCommand isComparator isDoStatement

isEol isExitIfStatement isExpression isFactor isFunctionCall isFunctionDefinition isInitializationBlock isLineAction isLoopStatement isMoveAction isMoveToAction

isMultiplyOperator isParameterList isProgram isReturnStatement isStatement isSwitchStatement isTerm isTurnAction isTurnToAction isVarDeclaration isVariable

Each of these methods should be spelled correctly (according to the Grammar), should be public boolean, and should take no arguments. Our JUnit tests will depend on each of these methods being present and being spelled correctly.

Each method should do one of three things:

• If the method recognizes the named nonterminal (and removes it from the incoming token stream), it should return true.
• If it can decide, after looking at a single token, that the named nonterminal cannot begin with that token, it should "push back" the token (so it can be used again), and return false.
• If the method decides, after looking at more than one token, that it cannot recognize the nonterminal, then it should throw a SyntaxException. It can do this by calling the error(String message) method with a suitable error message. (This is because the pushBack() method cannot recycle more than a single token.)

JUnit testing

Tokens form the foundation of the grammar. Low-level grammar rules, such as <term>, are built on these; higher-level rules, such as <expression>, are built on lower-level rules; and so on, all the way up to <program>. If <program> is to be correct, everything, all the way down, has to be correct. Hence, JUnit testing is essential.

You should test that each "is-Method" recognizes both simple and complex versions of the nonterminal it is intended to describe. In addition, you should test that each "is-Method" throws an exception when it should. However, you only need to check for SyntaxExceptions that should be thrown by the method you are testing, not by lower-level methods. For example, the isStatement() method checks for seven different statement types; you should check that isStatement() will recognize each of those statement types, but don't check for all the possible exceptions thrown by all seven statement types! Trust your JUnit tests of the seven statement types to do that for you.