Verify, TestYacas, LogicVerify , KnownFailure , RoundTo , VerifyArithmetic, VerifyDiv .

# The Yacas test suite

This chapter describes commands used for verifying correct performance of Yacas.

Verify, TestYacas, LogicVerify | verifying equivalence of two expressions
KnownFailure | Mark a test as a known failure
RoundTo | Round a real-valued result to a set number of digits
VerifyArithmetic, VerifyDiv | Special purpose arithmetic verifiers

Yacas comes with a test suite which can be found in the directory `tests/`. Typing

    make test

on the command line after Yacas was built will run the test. This test can be run even before `make install`, as it only uses files in the local directory of the Yacas source tree. The default extension for test scripts is `.yts` (Yacas test script).

The verification commands described in this chapter only display the expressions that do not evaluate correctly. Errors do not terminate the execution of the Yacas script that uses these testing commands, since they are meant to be used in test scripts.

###

Verify, TestYacas, LogicVerify -- verifying equivalence of two expressions

##### Standard library

##### Calling format:

    Verify(question,answer)
    TestYacas(question,answer)
    LogicVerify(question,answer)

##### Parameters:

`question` -- expression to check for

`answer` -- expected result after evaluation

##### Description:

The commands `Verify`, `TestYacas`, `LogicVerify` can be used to verify that an expression is equivalent to a correct answer after evaluation. All three commands return `True` or `False`.

For some calculations, the demand that two expressions are identical syntactically is too stringent. The Yacas system might change at various places in the future, but 1+x would still be equivalent, from a mathematical point of view, to x+1.

The general problem of deciding that two expressions a and b are equivalent, which is the same as saying that a-b=0 , is generally hard to decide on. The following commands solve this problem by having domain-specific comparisons.

The comparison commands do the following comparison types:

- `Verify` -- verify for literal equality. This is the fastest and simplest comparison, and can be used, for example, to test that an expression evaluates to 2.
- `TestYacas` -- compare two expressions after simplification as multivariate polynomials. If the two arguments are equivalent multivariate polynomials, this test succeeds. `TestYacas` uses `Simplify()`. Note: `TestYacas` currently should not be used to test equality of lists.
- `LogicVerify` -- Perform a test by using `CanProve` to verify that from `question` the expression `answer` follows. This test command is used for testing the logic theorem prover in Yacas.

##### Examples:

    In> Verify(1+2,3)
    Out> True;
    In> Verify(x*(1+x),x^2+x)
    ******************
    x*(x+1) evaluates to x*(x+1) which differs
      from x^2+x
    ******************
    Out> False;
    In> TestYacas(x*(1+x),x^2+x)
    Out> True;
    In> Verify(a And c Or b And Not c,a Or b)
    ******************
     a And c Or b And Not c evaluates to  a And c
      Or b And Not c which differs from  a Or b
    ******************
    Out> False;
    In> LogicVerify(a And c Or b And Not c,a Or b)
    Out> True;
    In> LogicVerify(a And c Or b And Not c,b Or a)
    Out> True;

##### See also:

Simplify , CanProve , KnownFailure .

###

KnownFailure -- Mark a test as a known failure

##### Standard library

##### Calling format:

    KnownFailure(test)

##### Parameters:

`test` -- expression that should return `False` on failure

##### Description:

The command `KnownFailure` marks a test as known to fail by displaying a message to that effect on screen.

This might be used by developers when they have no time to fix the defect, but do not wish to alarm users who download Yacas and type `make test`.

##### Examples:

    In> KnownFailure(Verify(1,2))
    Known failure:
    ******************
     1 evaluates to  1 which differs from  2
    ******************
    Out> False;
    In> KnownFailure(Verify(1,1))
    Known failure:
    Failure resolved!
    Out> True;

##### See also:

Verify , TestYacas , LogicVerify .

###

RoundTo -- Round a real-valued result to a set number of digits

##### Standard library

##### Calling format:

    RoundTo(number,precision)

##### Parameters:

`number` -- number to round off

`precision` -- precision to use for round-off

##### Description:

The function `RoundTo` rounds a floating point number to a specified precision, allowing for testing for correctness using the `Verify` command.

##### Examples:

    In> N(RoundTo(Exp(1),30),30)
    Out> 2.71828182110230114951959786552;
    In> N(RoundTo(Exp(1),20),20)
    Out> 2.71828182796964237096;

##### See also:

Verify , VerifyArithmetic , VerifyDiv .

###

VerifyArithmetic, VerifyDiv -- Special purpose arithmetic verifiers

##### Standard library

##### Calling format:

    VerifyArithmetic(x,n,m)
    RandVerifyArithmetic(n)
    VerifyDiv(u,v)

##### Parameters:

`x`, `n`, `m`, `u`, `v` -- integer arguments

##### Description:

The commands `VerifyArithmetic` and `VerifyDiv` test a mathematic equality which should hold, testing that the result returned by the system is mathematically correct according to a mathematically provable theorem.

`VerifyArithmetic` verifies for an arbitrary set of numbers x, n and m that

(x^n-1)*(x^m-1)=x^(n+m)-x^n-x^m+1.

The left and right side represent two ways to arrive at the same result, and so an arithmetic module actually doing the calculation does the calculation in two different ways. The results should be exactly equal.

`RandVerifyArithmetic(n)` calls `VerifyArithmetic()` with random values, `n` times.

`VerifyDiv(u,v)` checks that

u=v*Div(u,v)+Mod(u,v).

##### Examples:

    In> VerifyArithmetic(100,50,60)
    Out> True;
    In> RandVerifyArithmetic(4)
    Out> True;
    In> VerifyDiv(x^2+2*x+3,x+1)
    Out> True;
    In> VerifyDiv(3,2)
    Out> True;

##### See also:

Verify .