isValidColor test 1 (blue, should be true) = true
isValidColor test 2 (Blue, should be false) = false
isValidColor test 3 (yellow, should be true) = true
isValidColor test 4 (purple, should be false) = false

creating card c1 (red 4):
getColor: red
getValue: 4

creating card c2 (green 9):
getColor: green
getValue: 9

creating card c3 (blue 0):
getColor: blue
getValue: 0

changing card c3 to yellow 7:
getColor: yellow
getValue: 7

Trying to create a Card with a color of purple...
correctly threw an IllegalArgumentException...

Trying to create a Card with a value of -5...
correctly threw an IllegalArgumentException...

Trying to change c1's color to gold...
correctly threw an IllegalArgumentException...
c1 should still be red 4:
getColor: red
getValue: 4

Trying to change c2's value to 10...
correctly threw an IllegalArgumentException...
c2 should still be green 9:
getColor: green
getValue: 9