Pretty print unified diff with 5 line before/after window

Cargo.toml

@@ -11,5 +11,5 @@ keywords = ["test", "fixture"]
 categories = ["development-tools::testing"]
 
 [dependencies]
-difference = "2.0.0"
+similar = "2.1.0"
 newline-converter = "0.2.0"

src/lib.rs

@@ -33,8 +33,8 @@
 //! -Ten points for Gaston
 //! ```
 
-use difference::Changeset;
 use newline_converter::dos2unix;
+use similar::{udiff::unified_diff, Algorithm};
 use std::{env, fs, path::Path};
 
 /// Compare the contents of the file to the string provided
@@ -69,9 +69,14 @@ pub fn assert_contents<P: AsRef<Path>>(path: P, actual: &str) {
         let expected = dos2unix(&expected_s);
 
         if expected != actual {
-            let changeset =
-                Changeset::new(expected.as_ref(), actual.as_ref(), "\n");
-            println!("{}", changeset);
+            let diff = unified_diff(
+                Algorithm::Myers, // default algorithm used by git
+                &expected,
+                &actual,
+                5, // lines before and after
+                None,
+            );
+            println!("{}", diff);
             panic!(
                 r#"assertion failed: string doesn't match the contents of file: "{}" see diffset above
                 set EXPECTORATE=overwrite if these changes are intentional"#,

tests/data_a.txt

@@ -2,3 +2,23 @@ A eh?
 a a A
 a aye
 eh.
+
+A eh?
+a a A
+a aye
+eh.
+
+A eh?
+a a A
+a aye
+eh.
+
+A eh?
+a a A
+a aye
+eh.
+
+A eh?
+a a A
+a aye
+eh.

tests/data_a2.txt

@@ -0,0 +1,24 @@
+A eh?
+a a A
+a aye
+eh.
+
+A eh?
+a a A
+a aye
+eh.
+
+A eh?
+a a A
+a aye
+eh.
+
+A eh?
+this line changed
+a aye
+eh.
+
+A eh?
+a a A
+a aye
+eh.

tests/test_basic.rs

@@ -14,3 +14,10 @@ fn bad() {
     let actual = include_str!("data_a.txt");
     assert_contents("tests/data_b.txt", actual);
 }
+
+#[test]
+#[should_panic]
+fn one_line_change() {
+    let actual = include_str!("data_a.txt");
+    assert_contents("tests/data_a2.txt", actual);
+}