Add independent test for Vertical rustfmt-fn_args_density

tests/source/fn_args_density-vertical.rs

@@ -0,0 +1,33 @@
+// rustfmt-fn_args_density: Vertical
+
+// Empty list shoul stay on one line.
+fn do_bar(
+
+) -> u8 {
+    bar()
+}
+
+// A single argument should stay on the same line.
+fn do_bar(
+        a: u8) -> u8 {
+    bar()
+}
+
+// Multiple arguments should each get their own line.
+fn do_bar(a: u8, mut b: u8, c: &u8, d: &mut u8, closure: &Fn(i32) -> i32) -> i32 {
+    // This feature should not affect closures.
+    let bar = |x: i32, y: i32| -> i32 { x + y };
+    bar(a, b)
+}
+
+// If the first argument doesn't fit on the same line with the function name,
+// the whole list should probably be pushed to the next line with hanging
+// indent. That's not what happens though, so check current behaviour instead.
+// In any case, it should maintain single argument per line.
+fn do_this_that_and_the_other_thing(
+        aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa: u8,
+        b: u8, c: u8, d: u8) {
+    this();
+    that();
+    the_other_thing();
+}

tests/target/fn_args_density-vertical.rs

@@ -0,0 +1,36 @@
+// rustfmt-fn_args_density: Vertical
+
+// Empty list shoul stay on one line.
+fn do_bar() -> u8 {
+    bar()
+}
+
+// A single argument should stay on the same line.
+fn do_bar(a: u8) -> u8 {
+    bar()
+}
+
+// Multiple arguments should each get their own line.
+fn do_bar(a: u8,
+          mut b: u8,
+          c: &u8,
+          d: &mut u8,
+          closure: &Fn(i32) -> i32)
+          -> i32 {
+    // This feature should not affect closures.
+    let bar = |x: i32, y: i32| -> i32 { x + y };
+    bar(a, b)
+}
+
+// If the first argument doesn't fit on the same line with the function name,
+// the whole list should probably be pushed to the next line with hanging
+// indent. That's not what happens though, so check current behaviour instead.
+// In any case, it should maintain single argument per line.
+fn do_this_that_and_the_other_thing(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa: u8,
+                                    b: u8,
+                                    c: u8,
+                                    d: u8) {
+    this();
+    that();
+    the_other_thing();
+}