Extract helper functions for testing.

These functions help reduce duplication in the test harness and make it
easier to add tests for other write-modes in the future.

tests/system.rs

@@ -19,7 +19,7 @@ use std::io::{self, Read, BufRead, BufReader};
 use std::path::Path;
 
 use rustfmt::*;
-use rustfmt::filemap::write_system_newlines;
+use rustfmt::filemap::{write_system_newlines, FileMap};
 use rustfmt::config::{Config, ReportTactic, WriteMode};
 use rustfmt::rustfmt_diff::*;
 
@@ -65,12 +65,24 @@ fn coverage_tests() {
 
 #[test]
 fn checkstyle_test() {
-    let filename = "tests/source/fn-single-line.rs".to_string();
-    let expected = "tests/writemode/checkstyle.xml";
+    let filename = "tests/source/fn-single-line.rs";
+    let expected_filename = "tests/writemode/checkstyle.xml";
+    assert_output(filename, expected_filename, WriteMode::Checkstyle);
+}
 
-    let output = run_rustfmt(filename.clone(), WriteMode::Checkstyle);
 
-    let mut expected_file = fs::File::open(&expected)
+// Helper function for comparing the results of rustfmt
+// to a known output file generated by one of the write modes.
+fn assert_output(source: &str, expected_filename: &str, write_mode: WriteMode) {
+    let config = read_config(&source);
+    let file_map = run_rustfmt(source.to_string(), write_mode);
+
+    // Populate output by writing to a vec.
+    let mut out = vec![];
+    let _ = filemap::write_all_files(&file_map, &mut out, write_mode, &config);
+    let output = String::from_utf8(out).unwrap();
+
+    let mut expected_file = fs::File::open(&expected_filename)
                                 .ok()
                                 .expect("Couldn't open target.");
     let mut expected_text = String::new();
@@ -81,7 +93,7 @@ fn checkstyle_test() {
     let compare = make_diff(&expected_text, &output, DIFF_CONTEXT_SIZE);
     if compare.len() > 0 {
         let mut failures = HashMap::new();
-        failures.insert(filename, compare);
+        failures.insert(source.to_string(), compare);
         print_mismatches(failures);
         assert!(false, "Text does not match expected output");
     }
@@ -169,7 +181,7 @@ fn print_mismatches(result: HashMap<String, Vec<Mismatch>>) {
     assert!(t.reset().unwrap());
 }
 
-pub fn run_rustfmt(filename: String, write_mode: WriteMode) -> String {
+fn read_config(filename: &str) -> Config {
     let sig_comments = read_significant_comments(&filename);
     let mut config = get_config(sig_comments.get("config").map(|x| &(*x)[..]));
 
@@ -181,30 +193,21 @@ pub fn run_rustfmt(filename: String, write_mode: WriteMode) -> String {
 
     // Don't generate warnings for to-do items.
     config.report_todo = ReportTactic::Never;
+    config
+}
 
-    // Simulate run()
-    let mut out = Vec::new();
-    let file_map = format(Path::new(&filename), &config, write_mode);
-    let _ = filemap::write_all_files(&file_map, &mut out, write_mode, &config);
-    String::from_utf8(out).unwrap()
+// Simulate run()
+fn run_rustfmt(filename: String, write_mode: WriteMode) -> FileMap {
+    let config = read_config(&filename);
+    format(Path::new(&filename), &config, write_mode)
 }
 
 pub fn idempotent_check(filename: String,
                         write_mode: WriteMode)
                         -> Result<FormatReport, HashMap<String, Vec<Mismatch>>> {
     let sig_comments = read_significant_comments(&filename);
-    let mut config = get_config(sig_comments.get("config").map(|x| &(*x)[..]));
-
-    for (key, val) in &sig_comments {
-        if key != "target" && key != "config" {
-            config.override_value(key, val);
-        }
-    }
-
-    // Don't generate warnings for to-do items.
-    config.report_todo = ReportTactic::Never;
-
-    let mut file_map = format(Path::new(&filename), &config, write_mode);
+    let config = read_config(&filename);
+    let mut file_map = run_rustfmt(filename, write_mode);
     let format_report = fmt_lines(&mut file_map, &config);
 
     let mut write_result = HashMap::new();