Named parameters

Shouldn't the method call be test(a:'1', b:'2'); instead of test([a:'1',b:'2']);?

Please check Named parameters here.

Maybe I missed something, but I don't think Groovy has named parameters right now. There are discussions and proposals, but I'm not aware of anything official.

For your case, I think the map spread may help, but not in every case. Upon getting the values, it follows the order in which the map values were declared:

def test(String a, String b) { "a=$a, b=$b" }
def test(Map m) { test m*.value }

assert test(a: "aa", b:"bb") == "a=aa, b=bb"
assert test(b: "aa", a:"bb") != "a=aa, b=bb" // should be false :-(
assert test(b: "ccc", a:"ddd") == "a=ddd, b=ccc" // should have worked :-(

For classes, may I suggest Groovy's as operator?

@groovy.transform.CompileStatic
class Spread {
  class Person {
    String name
    BigDecimal height
  }

  def method(Person p) {
    "Name: ${p.name}, height: ${p.height}"
  }

  def method(Map m) { method m as Person }

  static main(String[] args) {
    assert new Spread().method(name: "John", height: 1.80) == 
      "Name: John, height: 1.80"
  }
}