added test for NaN for erf

Author: AhmedYKadah

test/erf.jl

@@ -20,6 +20,8 @@
             @test erf(T(-4.5))   ≈ T(-0.9999999998033839) rtol=2*eps(T)
             @test erf(T(-6))   ≈ T(-1.0) rtol=2*eps(T)
 
+            @test isnan(erf(T(NaN)))
+
             @test @inferred(erfc(T(1))) isa T
             @test erfc(T(1))  ≈ T(0.15729920705028513066) rtol=2*eps(T)