TestCases.txt

Single operation test:
1. 5+6=?	equals(add(5,6),11)
2. 6-3=?     	equals(sub(6,3),3)
3. 5*5=?	equals(mul(5,5),25)     	
4. 5*0=?	equals(mul(5,0),0)
5. 10/5		equals(div(10,5),2)
6. 10/0		equals(div(10,0),exeption)
7. 0/5		equals(div(0,5),0)

Testing the parser:
1. equals(add(5,add(5,5)),15)    5+5+5=15
2. equals(mul(5,mul(5,0)),0)     5*5*0=0
3. equals(div(10,div(8,4)),5)	10/5/2=1  	
4. equals(mul(5,mul("string",0)), "invalid input")	
5. equals(mul(5,mul(5,0)),0)
6. equals(add(5,-6),"invalid input")
7. equals(mul(5,"/6"),"invalid input") 5*/6 
8. equals(add(5,6),11)
9. "+5+9", "invalid input"


Multiple operation:
1. 5+2*2-1=8	equals(sub(add(5,mul(2,2)),1),8)	
2. 0/5+3-3+2=2	
3. 4-2*10/5=0
4. 4-1*3/0="can't divide by zero"

Parentheses:
1. 1+(4-4)=1
2. 5-5*(2/2)=0
3. (2+3)/5=1
4. 1+2*3+(1+3)/2=9
5.