test: initial test for onlyInstancesOf

__tests__/errors.test.js

@@ -0,0 +1,13 @@
+"use strict";
+
+const UsageError = require("../errors").UsageError;
+const onlyInstancesOf = require("../errors").onlyInstancesOf;
+
+describe("onlyInstancesOf", () => {
+  test("catches specified error", () => {
+    return Promise.reject(new UsageError("fake usage error"))
+      .catch(onlyInstancesOf(UsageError, (error) => {
+        expect(error).toBeInstanceOf(UsageError);
+      }));
+  });
+});

errors.js

@@ -1,18 +1,20 @@
 const ES6Error = require("es6-error");
 
-exports.onlyInstancesOf = function(errorType, handler) {
-  return(error) => {
+exports.onlyInstancesOf = function (errorType, handler) {
+  return (error) => {
     if (error instanceof errorType) {
       return handler(error);
+    // eslint-disable-next-line no-else-return
     } else {
       console.log(error.stack);
       process.exit(1);
     }
-  }
-}
+  };
+};
 
 exports.UsageError = class UsageError extends ES6Error {
+  // eslint-disable-next-line  no-useless-constructor
   constructor(message) {
     super(message);
   }
-}
+};