Added test of The Quotient Rule

Author: ivarne

test/symbolic.jl

@@ -7,6 +7,9 @@
 @assert isequal(differentiate(:(x + x), :x), 2)
 @assert isequal(differentiate(:(x - x), :x), 0)
 @assert isequal(differentiate(:(2 * x), :x), 2)
+@assert isequal(differentiate(:(2 / x), :x), :(-2 / x^2))
+@assert isequal(differentiate(:(x / 2), :x), 0.5)
+@assert isequal(differentiate(:(sin(x) / x), :x), :((cos(x) * x - sin(x)) / x^2))
 @assert isequal(differentiate(:(x * 2), :x), 2)
 @assert isequal(differentiate(:(a * x), :x), :a)
 @assert isequal(differentiate(:(x * a), :x), :a)