Refactor tests

Make use of the 'is' more to test the entire output.

Add test for no_color mode.

Replace several calls to format_string with calls that build a string
directly. I feel format_string is becoming unweildly and this simplfies
the tests

src/display.rs

@@ -9,6 +9,7 @@ static UNITS: [char; 4] = ['T', 'G', 'M', 'K'];
 pub struct DisplayData {
     pub short_paths: bool,
     pub is_reversed: bool,
+    pub colors_on: bool,
 }
 
 impl DisplayData {
@@ -76,7 +77,7 @@ pub fn draw_it(
     permissions: bool,
     use_full_path: bool,
     is_reversed: bool,
-    colors_on: bool,
+    no_colors: bool,
     root_node: Node,
 ) {
     if !permissions {
@@ -85,23 +86,16 @@ pub fn draw_it(
     let display_data = DisplayData {
         short_paths: !use_full_path,
         is_reversed,
+        colors_on: !no_colors,
     };
 
     for c in display_data.get_children_from_node(root_node) {
         let first_tree_chars = display_data.get_first_chars();
-        display_node(c, true, colors_on, first_tree_chars, &display_data)
+        display_node(c, true, first_tree_chars, &display_data)
     }
 }
 
-fn display_node(
-    node: Node,
-    is_biggest: bool,
-    colors_on: bool,
-    indent: &str,
-    display_data: &DisplayData,
-) {
-    let short = display_data.short_paths;
-
+fn display_node(node: Node, is_biggest: bool, indent: &str, display_data: &DisplayData) {
     let mut num_siblings = node.children.len() as u64;
     let max_sibling = num_siblings;
     let new_indent = clean_indentation_string(indent);
@@ -109,7 +103,7 @@ fn display_node(
     let size = node.size;
 
     if !display_data.is_reversed {
-        print_this_node(&*name, size, is_biggest, short, colors_on, indent);
+        print_this_node(&*name, size, is_biggest, display_data, indent);
     }
 
     for c in display_data.get_children_from_node(node) {
@@ -117,11 +111,11 @@ fn display_node(
         let chars = display_data.get_tree_chars(num_siblings, max_sibling, !c.children.is_empty());
         let is_biggest = display_data.is_biggest(num_siblings, max_sibling);
         let full_indent = new_indent.clone() + chars;
-        display_node(c, is_biggest, colors_on, &*full_indent, display_data)
+        display_node(c, is_biggest, &*full_indent, display_data)
     }
 
     if display_data.is_reversed {
-        print_this_node(&*name, size, is_biggest, short, colors_on, indent);
+        print_this_node(&*name, size, is_biggest, display_data, indent);
     }
 }
 
@@ -146,34 +140,25 @@ fn print_this_node(
     name: &str,
     size: u64,
     is_biggest: bool,
-    short_paths: bool,
-    colors_on: bool,
+    display_data: &DisplayData,
     indentation: &str,
 ) {
     let pretty_size = format!("{:>5}", human_readable_number(size),);
     println!(
         "{}",
-        format_string(
-            name,
-            is_biggest,
-            short_paths,
-            colors_on,
-            &*pretty_size,
-            indentation
-        )
+        format_string(name, is_biggest, display_data, &*pretty_size, indentation)
     )
 }
 
 pub fn format_string(
     dir_name: &str,
     is_biggest: bool,
-    short_paths: bool,
-    colors_on: bool,
+    display_data: &DisplayData,
     size: &str,
     indentation: &str,
 ) -> String {
     let printable_name = {
-        if short_paths {
+        if display_data.short_paths {
             dir_name.split('/').last().unwrap_or(dir_name)
         } else {
             dir_name
@@ -181,7 +166,7 @@ pub fn format_string(
     };
     format!(
         "{} {} {}",
-        if is_biggest && colors_on {
+        if is_biggest && display_data.colors_on {
             Fixed(196).paint(size)
         } else {
             Style::new().paint(size)