X2: initial tests

Complete the following tests for X2.html, adding to the test cases already in the provided X0. They should be complete, running tests (even though they may not pass yet, and eval etc. might throw exceptions). But do have any new needed data definitions/classes with their fields, even if no code for them). On D2L, submit just your test-files containing this code (new data definitions/classes not needed).
Since you need to do X1 in both racket and Java, you need X1 tests for both languages (#1,#2). However, for X2, you only need test cases for the language you are using for X2 (#3a or #3b).
Attach two files: the racket tests in one file, and the Java tests in another. (You can add these to the existing test files distributed with X0.)
You don't need to include the further files needed to actually run (even though you should be able to actually run these files, of course).

When filling in the blanks below, the result of string->expr will be fairly verbose (spanning more than one line), but will also be the most informative in understanding how the code works.

solution (available after class on Wed.).

some X1 tests, racket

You might insert your tests below into to the provided file X0-tests.rkt (and perhaps update the file-name to indicate that it now includes X1 and X2 tests).

(require rackunit)

(define prog0 "~8.1 mod [3]!")
(check-equal? (string->expr prog0)                                                                                                                                )
(check-equal? (expr->string (string->expr prog0))                                              )
(check-equal? (eval (string->expr prog0))           )


; Now, make a test for a IfPos expression.
; You only need one example for this submission, but
; in your real program you'll probably want at least three.

some X1 tests, Java

You might add the following to the file ExprTest.java.

@Test
void testAFew() {
  String prog0 = "~8.1 mod [3]!";
  assertEquals( Expr.parse(prog0), new BinOp(                                                                                                                                ) );
  assertEquals( Expr.parse(prog0).toString(),                                              );
  assertEquals( Expr.parse(prog0).eval(),                                      );


  // Now, make a test for a `ifPos` expression.
  // You only need one example for this submission, but
  // in your real program you'll probably want at least two or three.
  
  }

If you are using JUnit (see how to run JUnit), these tests should work directly. Otherwise, you might want to write your own method

void assertEquals( Object actual,  Object expected ) {
  if (!actual.equals(expected)) {
    System.err.printf("assertion failed:\nExpect: %s\nActual: %s\n", expected.toString(), actual.toString() );
    }
  }

It is not a requirement to use JUnit for this assignment.

For X2, you'll use either racket or Java (that is, only complete (a) or (b)):

X2 tests, racket

(define prog2 "let x <- 5 in ~4 mlt x!") ;
(check-equal? (string->expr prog2)                                                                                                                                           )
(check-equal? (expr->string (string->expr prog2))                )
(check-equal? (eval (string->expr prog2))         )

; Make an additional example, where the `let` is *not* the top-level expression:
; Then, have the three tests for it, as above.







; For X2, the item B.iv mentions that you'll have to do substitution in a tree.
; Although `substitute` returns a *tree* (an Expr),
; we can use `string->expr` (already tested!) to help us generate our expected-results.
;
(check-equal? (substitute "x" 9 (string->expr "3"))   (string->expr         ) )
(check-equal? (substitute "x" 9 (string->expr "x"))   (string->expr         ) )
(check-equal? (substitute "z" 7 (string->expr "x"))   (string->expr         ) )
(check-equal? (substitute "z" 7 (string->expr "~4 sub z!"))   (string->expr                                 ) )
(check-equal? (substitute "z" 7 (string->expr "let x <- z in ~x mod z!"))
              (string->expr                                                                           ) )

; Give at least one more interesting tree, to test `substitute` on,
; with parse-tree of height of 2 or more.
; You do *not* need to do `substitute` on a parse tree containing a `let` inside of it ... yet.
; (But you are encouraged to start thinking about what you want to happen, in that situation.)

some X2 tests, Java

String prog2 = "let x <- 5 in ~4 mlt x!";
assertEquals( Expr.parse(prog2),                                                                                                                                                                                                                                                          );
assertEquals( Expr.parse(prog2).toString(),                );
assertEquals( Expr.parse(prog2).eval(),                                  );
/*
 ; Make an example, where the `let` is *not* the top-level expression:
 ; Then, have the three tests for it, as above.
*/






/*
 ; For X2, item B.iv mentions that you'll have to do substitution in a tree.
 ; Although `substitute` returns a *tree* (an Expr),
 ; we can use `parse` (already tested!) to help us generate our expected-results.
*/
assertEquals( Expr.parse("3").substitute(new Id("x"),new Num(9)), Expr.parse(         ) );
assertEquals( Expr.parse("x").substitute(new Id("x"),new Num(9)), Expr.parse(         ) );
assertEquals( Expr.parse("x").substitute(new Id("z"),new Num(7)), Expr.parse(         ) );
assertEquals( Expr.parse("~4 sub z!").substitute(new Id("z"),new Num(7)), Expr.parse(                                ) );
assertEquals( Expr.parse("let x <- z in ~x mlt z!").substitute(new Id("z"),new Num(7)),
              Expr.parse(                                                                           ) );
/*
 ; Give at least one more interesting tree, to test `substitute` on,
 ; with parse-tree of height 2 or more.
 ; You do *not* need to do `substitute` on a parse tree containing a `let` inside of it ... yet.
 ; (But you are encouraged to start thinking about what you want to happen, in that situation.)
*/

This code should compile and run, though of course they won't yet pass.
Note that before these tests compile/run, you'll need to define the structs/classes for Id and LetExprs. You don't need to submit those /structs classes with the test cases but presumably you'll at least have the class-with-field declarations, and (for Java) the routine constructor. Note that you don't need to write any getters for your Java fields, but you'll eventually need to write an equals and hashCode method, as done in the provided X0 classes.

These tests are not meant to be comprehensive of everything you'll eventually want to test for. They are just intended to get you started on the homework, and understanding what the functions need to do, before the weekend.

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