Add test to simulate typing each test file to validate handling of partial input.

test/markdownlint-test.js

@@ -647,3 +647,23 @@ module.exports.doc = function doc(test) {
       test.done();
     });
 };
+
+module.exports.typeAllFiles = function typeAllFiles(test) {
+  // Simulates typing each test file to validate handling of partial input
+  var files = fs.readdirSync("./test");
+  files.forEach(function forFile(file) {
+    if (/\.md$/.test(file)) {
+      var content = fs.readFileSync(
+        path.join("./test", file), shared.utf8Encoding);
+      while (content) {
+        markdownlint.sync({
+          "strings": {
+            "content": content
+          }
+        });
+        content = content.slice(0, -1);
+      }
+    }
+  });
+  test.done();
+};