Provide a default isapprox method for ring elements

src/Rings.jl

@@ -8,6 +8,16 @@ function isequal(a::RingElem, b::RingElem)
    return parent(a) == parent(b) && a == b
 end
 
+# Implement `isapprox` for ring elements via equality by default. On the one
+# hand, we need isapprox methods to be able to conformance test series rings.
+# On the other hand this is essentially the only sensible thing to do in
+# positive characteristic so we might as well do it in a generic method.
+function Base.isapprox(x::NCRingElem, y::NCRingElem;
+                       atol::Real=0, rtol::Real=0,
+                       nans::Bool=false, norm::Function=abs)
+    return x == y
+end
+
 """
     divexact(x, y; check::Bool=true)