Fix incorrect operate test set (#242)

test/interface.jl

@@ -95,16 +95,32 @@ end
 end
 
 @testset "operate" begin
- @testset "$(typeof(x))" for x in [2, big(3)]
- @testset "$op" for op in [+, *, gcd, lcm]
- @test MA.operate(op, x) !== x
+ @testset "$T" for T in (Int, BigInt, Rational{Int})
+ x = T(7)
+ @testset "1-ary $op" for op in [+, *, gcd, lcm]
+ a = op(x)
+ b = MA.operate(op, x)
+ @test a == b
+ if MA.mutability(T, op, T) == MA.IsMutable()
+ @test a !== b
+ end
  end
  ops = [+, *, MA.add_mul, MA.sub_mul, MA.add_dot, gcd, lcm]
- @testset "$op" for op in ops
- @test MA.operate(op, x, x, x, x) !== op(x, x, x, x)
+ @testset "4-ary $op" for op in ops
+ a = op(x, x, x, x)
+ b = MA.operate(op, x, x, x, x)
+ @test a == b
+ if MA.mutability(T, op, T, T, T, T) == MA.IsMutable()
+ @test a !== b
+ end
  end
- @testset "$op" for op in [-, /, div]
- @test MA.operate(op, x, x) !== op(x, x)
+ @testset "2-ary $op" for op in [-, /, div]
+ a = op(x, x)
+ b = MA.operate(op, x, x)
+ @test a == b
+ if MA.mutability(T, op, T, T) == MA.IsMutable()
+ @test a !== b
+ end
  end
  end
 end