Add initial tests for false/true.

Makefile

@@ -164,6 +164,7 @@ TEST_PROGS  := \
   dirname \
   echo \
   factor \
+  false \
   fold \
   mkdir \
   mv \
@@ -173,6 +174,7 @@ TEST_PROGS  := \
   sort \
   test \
   tr \
+  true \
   truncate \
   unexpand
 

test/false.rs

@@ -0,0 +1,9 @@
+use std::process::Command;
+
+static PROGNAME: &'static str = "./false";
+
+#[test]
+fn test_exit_code() {
+    let exit_status = Command::new(PROGNAME).status().unwrap().success();
+    assert_eq!(exit_status, false);
+}

test/true.rs

@@ -0,0 +1,9 @@
+use std::process::Command;
+
+static PROGNAME: &'static str = "./true";
+
+#[test]
+fn test_exit_code() {
+    let exit_status = Command::new(PROGNAME).status().unwrap().success();
+    assert_eq!(exit_status, true);
+}