Code review changes.

test/number/from_string.wren

@@ -3,6 +3,11 @@ IO.print(Num.fromString("-123") == -123) // expect: true
 IO.print(Num.fromString("-0") == -0) // expect: true
 IO.print(Num.fromString("12.34") == 12.34) // expect: true
 IO.print(Num.fromString("-0.0001") == -0.0001) // expect: true
+IO.print(Num.fromString(" 12 ") == 12) // expect: true
+IO.print(Num.fromString("1.2prefix") == 1.2) // expect: true
 
-// Test a non-number literal and ensure it returns null.
+// Test some non-number literals and ensure they return null.
 IO.print(Num.fromString("test1") == null) // expect: true
+IO.print(Num.fromString("") == null) // expect: true
+IO.print(Num.fromString("prefix1.2") == null) // expect: true
+

test/number/from_string_not_string.wren

@@ -0,0 +1 @@
+Num.fromString(1) // expect runtime error: Argument must be a string.