adding more tests and doc updates

Configurations.md

@@ -1061,12 +1061,14 @@ This option is currently ignored for stdin (`@generated` in stdin is ignored.)
 
 ## `generated_file_header_size`
 
-Number of lines to check for a `@generated` pragma header when `format_generated_files` is enabled. When `format_generated_files` is disabled, this option has no effect.
+Number of lines to check for a `@generated` pragma header when `format_generated_files` is `false`. When `format_generated_files` is `true`, this option has no effect.
 
 - **Default value**: `5`
 - **Possible values**: any positive integer
 - **Stable**: No (tracking issue: [#5080](https://github.com/rust-lang/rustfmt/issues/5080))
 
+See also [format_generated_files](#format_generated_files) link here.
+
 ## `format_macro_matchers`
 
 Format the metavariable matching patterns in macros.

tests/source/configs/format_generated_files/false_with_marker_out_scope_size.rs

@@ -0,0 +1,10 @@
+// rustfmt-format_generated_files: false
+// rustfmt-generated_file_header_size: 1
+
+fn main()
+{
+    println!("hello, world")
+    ;
+}
+
+// @generated

tests/source/configs/format_generated_files/true_with_marker_in_scope_size.rs

@@ -0,0 +1,10 @@
+// rustfmt-format_generated_files: true
+// rustfmt-generated_file_header_size: 20
+
+fn main()
+{
+    println!("hello, world")
+    ;
+}
+
+// @generated

tests/target/configs/format_generated_files/false_with_marker_out_scope_size.rs

@@ -0,0 +1,8 @@
+// rustfmt-format_generated_files: false
+// rustfmt-generated_file_header_size: 1
+
+fn main() {
+    println!("hello, world");
+}
+
+// @generated

tests/target/configs/format_generated_files/true_with_marker_in_scope_size.rs

@@ -0,0 +1,8 @@
+// rustfmt-format_generated_files: true
+// rustfmt-generated_file_header_size: 20
+
+fn main() {
+    println!("hello, world");
+}
+
+// @generated