Add tests

Author: captbaritone

tests/source/configs/format_generated_files/false_with_generated_file_header_size.rs

@@ -0,0 +1,10 @@
+// rustfmt-format_generated_files: false
+// rustfmt-generated_file_header_size: 15
+
+fn main()
+{
+    println!("hello, world")
+    ;
+}
+
+// @generated

tests/source/configs/format_generated_files/true_with_marker_not_in_header.rs

@@ -0,0 +1,9 @@
+// rustfmt-format_generated_files: true
+
+fn main()
+{
+    println!("hello, world")
+    ;
+}
+
+// @generated

tests/target/configs/format_generated_files/false_with_generated_file_header_size.rs

@@ -0,0 +1,10 @@
+// rustfmt-format_generated_files: false
+// rustfmt-generated_file_header_size: 15
+
+fn main()
+{
+    println!("hello, world")
+    ;
+}
+
+// @generated

tests/target/configs/format_generated_files/true_with_marker_not_in_header.rs

@@ -0,0 +1,7 @@
+// rustfmt-format_generated_files: true
+
+fn main() {
+    println!("hello, world");
+}
+
+// @generated