Add snapshot testing

tests/snapshots/sample.modified.rs

@@ -18,4 +18,4 @@ fn area(rectangle: &Rectangle) -> u32 {
 
 fn perimeter(rectangle: &Rectangle) -> u32 {
     (rectangle.width + rectangle.height) * 2
-}
+}

tests/tester.rs

@@ -0,0 +1,75 @@
+use std::env;
+use std::fs::{self, File};
+use std::io::Read;
+use std::path::PathBuf;
+use std::process::Command;
+
+pub struct BatTester {
+    exe: PathBuf,
+}
+
+impl BatTester {
+    pub fn new() -> Self {
+        modify_sample_file();
+        // Lifted from fd :)
+        let root = env::current_exe()
+            .expect("tests executable")
+            .parent()
+            .expect("tests executable directory")
+            .parent()
+            .expect("bat executable directory")
+            .to_path_buf();
+
+        let exe_name = if cfg!(windows) { "bat.exe" } else { "bat" };
+
+        BatTester {
+            exe: root.join(exe_name),
+        }
+    }
+
+    pub fn test_snapshot(&self, style: &str) {
+        let output = Command::new(&self.exe)
+            .args(&[
+                "tests/snapshots/sample.rs",
+                &format!("--style={}", style),
+            ])
+            .output()
+            .expect("bat failed");
+        // have to do the replace because the filename in the header changes based on the current working directory
+        let actual = String::from_utf8_lossy(&output.stdout)
+            .as_ref()
+            .replace("tests/snapshots/", "");
+
+        let mut expected = String::new();
+        let mut file = File::open(format!("tests/snapshots/output/{}.snapshot.txt", style))
+            .expect("snapshot file missing");
+        file.read_to_string(&mut expected)
+            .expect("could not read snapshot file");
+
+        assert_eq!(expected, actual);
+    }
+}
+
+impl Drop for BatTester {
+    fn drop(&mut self) {
+        undo_sample_file_modification();
+    }
+}
+
+fn modify_sample_file() {
+    fs::copy(
+        "tests/snapshots/sample.modified.rs",
+        "tests/snapshots/sample.rs",
+    ).expect("generating modified sample file failed");
+}
+
+fn undo_sample_file_modification() {
+    let output = Command::new("git")
+        .args(&["checkout", "--", "tests/snapshots/sample.rs"])
+        .output()
+        .expect("git checkout failed");
+
+    if !output.status.success() {
+        panic!("undoing modified sample changes failed")
+    }
+}

tests/tests.rs

@@ -0,0 +1,33 @@
+mod tester;
+
+use tester::BatTester;
+
+static STYLES: &'static [&'static str] = &[
+    "changes",
+    "grid",
+    "header",
+    "numbers",
+    "changes,grid",
+    "changes,header",
+    "changes,numbers",
+    "grid,header",
+    "grid,numbers",
+    "header,numbers",
+    "changes,grid,header",
+    "changes,grid,numbers",
+    "changes,header,numbers",
+    "grid,header,numbers",
+    "changes,grid,header,numbers",
+    "full",
+    "plain",
+];
+
+#[test]
+fn test_snapshots() {
+    let bat_tester = BatTester::new();
+
+    for style in STYLES {
+        println!("testing {}", style);
+        bat_tester.test_snapshot(&*style);
+    }
+}