TriangleTester written by S. Robbins
Creating triangle to test accessor and toString methods:
toString gives: Triangle with sides 3.1, 4.2, and 5.7
The sides of this triangle are 3.1, 4.2, and 5.7
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The following are for testing the valid method:
The first 5 should all be valid
1. right triangle: sides[3.0,4.0,5.0] is valid
2. equilateral triangle: sides[3.0,3.0,3.0] is valid
3. isoceles triangle: sides[3.0,4.0,4.0] is valid
4. obtuse triangle: sides[3.0,4.0,6.0] is valid
5. this one is just OK: sides[9.0,4.01,5.0] is valid

The rest should all be invalid
6. first side just too large: sides[9.0,4.0,5.0] is not valid
7. second side just too large: sides[3.0,8.0,5.0] is not valid
8. third side just too large: sides[3.0,4.0,7.0] is not valid
9. not valid: sides[4.21,11.87,6.341] is not valid
10. one side negative: sides[3.0,-4.0,5.0] is not valid
11. two sides negative: sides[-3.0,-4.0,5.0] is not valid
12. three sides negative: sides[-3.0,-4.0,-5.0] is not valid
10. one side zero: sides[3.0,0.0,5.0] is not valid
11. two sides zero: sides[0.0,0.0,5.0] is not valid
12. three sides zero: sides[0.0,0.0,0.0] is not valid