code: def test_significant():
      """Test significant formatter"""
      f = formatters.significant
      assert f(1) == "1"
      assert f(1.0) == "1"
      assert f(-1.0) == "-1"
      assert f(10) == "10"
      assert f(10000000000) == "1e+10"
      assert f(100000000000) == "1e+11"
      assert f(120000000000) == "1.2e+11"
  
      assert f(0.1) == "0.1"
      assert f(0.01) == "0.01"
      assert f(0.0000000001) == "1e-10"
      assert f(-0.0000000001) == "-1e-10"
      assert f(0.0000000001002) == "1.002e-10"
  
      assert f(0.0000000001002) == "1.002e-10"
  
      assert f(0.12345678912345) == "0.1234567891"
      assert f(0.012345678912345) == "0.01234567891"
  
      assert f(12345678912345) == "1.234567891e+13"
  
label_desc: Use image node_id 3 for calling a global function with example usage: test_significant() without return types