tests: fix BOM issue

Basically, the problem here is that the quickcheck tests will sometimes
generate CSV data that begins with a UTF-8 BOM and the CSV reader
automatically strips it.

There's a better way to solve this by making tests more robust, but they
were written without this consideration. As a hack, we just make sure
that we don't generate CSV data that begins with a BOM.

This isn't quite 100% correct since we could still get CSV data
beginning with a UTF-8 BOM through shrinking, but that only occurs when
a legitimate test failure happens. So this could potentially make
failure modes worse, but we abide for now.

Fixes #227

tests/test_cat.rs

@@ -1,6 +1,7 @@
 use std::process;
 
 use {Csv, CsvData, qcheck};
+use quickcheck::TestResult;
 use workdir::Workdir;
 
 fn no_headers(cmd: &mut process::Command) {
@@ -72,7 +73,7 @@ fn cat_rows_headers() {
 
 #[test]
 fn prop_cat_cols() {
-    fn p(rows1: CsvData, rows2: CsvData) -> bool {
+    fn p(rows1: CsvData, rows2: CsvData) -> TestResult {
         let got: Vec<Vec<String>> = run_cat(
             "cat_cols", "columns", rows1.clone(), rows2.clone(), no_headers);
 
@@ -83,9 +84,10 @@ fn prop_cat_cols() {
             r1.extend(r2.into_iter());
             expected.push(r1);
         }
-        rassert_eq!(got, expected)
+        assert_eq!(got, expected);
+        TestResult::passed()
     }
-    qcheck(p as fn(CsvData, CsvData) -> bool);
+    qcheck(p as fn(CsvData, CsvData) -> TestResult);
 }
 
 #[test]

tests/tests.rs

@@ -87,6 +87,10 @@ impl ops::Deref for CsvRecord {
     fn deref<'a>(&'a self) -> &'a [String] { &*self.0 }
 }
 
+impl ops::DerefMut for CsvRecord {
+    fn deref_mut<'a>(&'a mut self) -> &'a mut [String] { &mut *self.0 }
+}
+
 impl fmt::Debug for CsvRecord {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let bytes: Vec<_> = self.iter()
@@ -139,13 +143,21 @@ impl Arbitrary for CsvData {
     fn arbitrary<G: Gen>(g: &mut G) -> CsvData {
         let record_len = { let s = g.size(); g.gen_range(1, s) };
         let num_records: usize = g.gen_range(0, 100);
-        CsvData{
+        let mut d = CsvData{
             data: (0..num_records).map(|_| {
                 CsvRecord((0..record_len)
                           .map(|_| Arbitrary::arbitrary(g))
                           .collect())
             }).collect(),
+        };
+        // If the CSV data starts with a BOM, strip it, because it wreaks havoc
+        // with tests that weren't designed to handle it.
+        if !d.data.is_empty() && !d.data[0].is_empty() {
+            if let Some(stripped) = d.data[0][0].strip_prefix("\u{FEFF}") {
+                d.data[0][0] = stripped.to_string();
+            }
         }
+        d
     }
 
     fn shrink(&self) -> Box<Iterator<Item=CsvData>+'static> {