ripgrep: use exit code 2 to indicate error

Exit code 1 was shared to indicate both "no results" and "error." Use
status code 2 to indicate errors, similar to grep's behavior.

Fixes #948 

PR #954

tests/workdir.rs

@@ -261,18 +261,37 @@ impl WorkDir {
     pub fn assert_err(&self, cmd: &mut process::Command) {
         let o = cmd.output().unwrap();
         if o.status.success() {
-            panic!("\n\n===== {:?} =====\n\
-                    command succeeded but expected failure!\
-                    \n\ncwd: {}\
-                    \n\nstatus: {}\
-                    \n\nstdout: {}\n\nstderr: {}\
-                    \n\n=====\n",
-                   cmd, self.dir.display(), o.status,
-                   String::from_utf8_lossy(&o.stdout),
-                   String::from_utf8_lossy(&o.stderr));
+            panic!(
+                "\n\n===== {:?} =====\n\
+                 command succeeded but expected failure!\
+                 \n\ncwd: {}\
+                 \n\nstatus: {}\
+                 \n\nstdout: {}\n\nstderr: {}\
+                 \n\n=====\n",
+                cmd,
+                self.dir.display(),
+                o.status,
+                String::from_utf8_lossy(&o.stdout),
+                String::from_utf8_lossy(&o.stderr)
+            );
         }
     }
 
+    /// Runs the given command and asserts that its exit code matches expected exit code.
+    pub fn assert_exit_code(&self, expected_code: i32, cmd: &mut process::Command) {
+        let code = cmd.status().unwrap().code().unwrap();
+
+        assert_eq!(
+            expected_code, code,
+            "\n\n===== {:?} =====\n\
+             expected exit code did not match\
+             \n\nexpected: {}\
+             \n\nfound: {}\
+             \n\n=====\n",
+            cmd, expected_code, code
+        );
+    }
+
     /// Runs the given command and asserts that something was printed to
     /// stderr.
     pub fn assert_non_empty_stderr(&self, cmd: &mut process::Command) {