Add initial tests for echo.

Makefile

@@ -162,6 +162,7 @@ TEST_PROGS  := \
   cp \
   env \
   dirname \
+  echo \
   factor \
   fold \
   mkdir \

test/echo.rs

@@ -0,0 +1,50 @@
+use std::process::Command;
+use std::str;
+
+static PROGNAME: &'static str = "./echo";
+
+#[test]
+fn test_default() {
+    let po = Command::new(PROGNAME)
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap();
+    assert_eq!(out, "\n");
+}
+
+#[test]
+fn test_no_trailing_newline() {
+    let po = Command::new(PROGNAME)
+        .arg("-n")
+        .arg("hello_world")
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap();
+    assert_eq!(out, "hello_world");
+}
+
+#[test]
+fn test_enable_escapes() {
+    let po = Command::new(PROGNAME)
+        .arg("-e")
+        .arg("\\\\\\t\\r")
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap();
+    assert_eq!(out, "\\\t\r\n");
+}
+
+#[test]
+fn test_disable_escapes() {
+    let po = Command::new(PROGNAME)
+        .arg("-E")
+        .arg("\\b\\c\\e")
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap();
+    assert_eq!(out, "\\b\\c\\e\n");
+}