Escape test names in events emitted by the JSON formatter

Converts test names to escaped strings before formatting the message to be
emitted. This prevents invalid JSON being generated when the test name contains
text that needs escaped (e.g.: the backslash in a Windows path from a doctest).

Author: garyttierney

libtest/formatters/json.rs

@@ -26,12 +26,17 @@ impl<T: Write> JsonFormatter<T> {
         if let Some(extras) = extra {
             self.write_message(&*format!(
                 r#"{{ "type": "{}", "name": "{}", "event": "{}", {} }}"#,
-                ty, name, evt, extras
+                ty,
+                EscapedString(name),
+                evt,
+                extras
             ))
         } else {
             self.write_message(&*format!(
                 r#"{{ "type": "{}", "name": "{}", "event": "{}" }}"#,
-                ty, name, evt
+                ty,
+                EscapedString(name),
+                evt
             ))
         }
     }
@@ -48,7 +53,7 @@ impl<T: Write> OutputFormatter for JsonFormatter<T> {
     fn write_test_start(&mut self, desc: &TestDesc) -> io::Result<()> {
         self.write_message(&*format!(
             r#"{{ "type": "test", "event": "started", "name": "{}" }}"#,
-            desc.name
+            EscapedString(desc.name.as_slice())
         ))
     }