Groovy scripts raises an error:
def a = "test"
No signature of method: java.lang.String.positive() is
applicable for argument types: () values: 
def a = new String(
As groovy doesn't have EOL marker (such as
;) it gets confused if you put the operator on the following line
This would work instead:
def a = "test" + "test" + "test"
as the Groovy parser knows to expect something on the following line
Groovy sees your original
def as three separate statements. The first assigns
a, the second two try to make
"test" positive (and this is where it fails)
new String constructor method, the Groovy parser is still in the constructor (as the brace hasn't yet closed), so it can logically join the three lines together into a single statement
For true multi-line Strings, you can also use the triple quote:
def a = """test test test"""
Will create a String with test on three lines
Also, you can make it neater by:
def a = """test |test |test""".stripMargin()
stripMargin method will trim the left (up to and including the
| char) from each line