Fix

Author: blegat

test/substitution.jl

@@ -103,7 +103,6 @@ import MutableArithmetics as MA
         t = T(1) * x[1]
         @test copy(t).coefficient !== t.coefficient
         @test MA.mutable_copy(t).coefficient !== t.coefficient
-        @test MA.copy_if_mutable(t).coefficient !== t.coefficient
         F = T(5) * x[1] * x[2] * x[3] + T(1) * x[1] * x[2]^2
         @test subs(F, x[3] => T(0)) == x[1] * x[2]^2
         @test subs(F, x[3] => 0) == x[1] * x[2]^2