Timecop: reset after each test

Timecop is a great gem to set the current time in tests. However, it is easy to introduce flakyness to your test suite when you forget to reset the time after the test.
This might be the case if:

  • a test freezes time and a later test does not work for frozen time
  • a later test needs the real current date to work correctly

Often you only notice these kinds of errors in rare cases when tests are executed in a particular order.

A way to avoid this is by using block notation (`Timecop.travel(...) ...

Jasmine: Mocking ESM imports

In a Jasmine spec you want to spy on a function that is imported by the code under test. This card explores various methods to achieve this.


We are going to use the same example to demonstrate the different approaches of mocking an imported function.

We have a module 'lib' that exports a function hello():

// lib.js

function hello() {
  console.log("hi world")

export hello

We have a second module 'client' that exports a function helloTwice(). All this does is call hello() ...

Heads up: network requests `Kernel#open` are not mocked with VCR

We usually rely on VCR and WebMock to prevent any real network connection when running our unit tests.

This is not entirely true: They are both limited to a set of HTTP libraries listed below (as of 2022). Direct calls to Kernel#open or OpenURI#open_uri are not mocked and will trigger real network requests even in tests. This might bite you e.g. in [older versions of CarrierWave](https://github.com/carrierwaveuploader/carrierwave/blob/0.11-stable/lib/carrierwave/upl...

subscript, superscript and line-heights

By default subscript (<sub></sub>) and superscript (<sup></sup>) tags are styled with vertical-align: sub, respectively vertical-align: super by most browsers.
However, without adaptations, this will probably break your line-heights.

A common suggestion is to style those two tags accordingly:

sup, sub {
  vertical-align: baseline;
  position: relative;
  top: -0.4em;  /* can be adapted according to preferences */
sub {  

A modern approach to SVG icons

You have some SVG files you want to use as icons on your website. How would you embed them?

Common options are:

  1. Use them with an image: <img src='path-to-icon.svg'>
  2. Embed them inline with <svg>$ICON</svg>
  3. Embed them using CSS and background-image: url(path-to-icon.svg) or even background-image: url(data:$ICON).
  4. Build your own icon font.

All of these have drawbacks:

  • Image and background-image do not allow to recolor the image using CSS.
  • Inline-<svg> are unnecessary work for the server and are...

Using path aliases in esbuild

In esbuild, you usually import other files using relative paths:

import './some-related-module'
import `../../utils/some-utility-module`
import `../../../css/some-css.sass`

This is totally fine if you import closely related files, but a bit clunky when you're trying to import some "global" module, like a utility module. When moving a file, your imports also need to change.

To get around this, esbuild support a mechanism first introduced in TypeScript called "path aliases". It works like this:

First, you create a file called `js...

Jasmine: Creating DOM elements efficiently

Jasmine specs for the frontend often need some DOM elements to work with. Because creating them is such a common task, we should have an efficient way to do it.

Let's say I need this HTML structure:

<ul type="square">
  <li>item 1</li>
  <li>item 2</li>

This card compares various approaches to fabricating DOM elements for testing.

Constructing individual elements

While you can use standard DOM functions to individually create and append elements, this is extremely verbose:

let list = document.createElement('...

Jasmine: Cleaning up the DOM after each test

Jasmine specs that work with DOM elements often leave elements in the DOM after they're done. This will leak test-local DOM state to subsequent tests.

For example, this test creates a <spoiler-text> element, runs some expectations, and then forgets to remove it from the DOM:

describe('<spoiler-text>', function() {
  it ('hides the secret until clicked', function() {
    let element = document.createElement('spoiler-text')
    element.secret = 'The butler did it'

Chrome DevTools: Treasure (Overview)


The Chrome DevTools are a neat collection of tools for the daily work as a web developer. If you're lucky, you'll maybe find some handy stuff in here.



  • [Breakpoints on HTML Elements](https://makandracards.com/makandra/517982-chrome-devtools...

Careful when using Time objects for generating ETags

You can use ETags to allow clients to use cached responses, if your application would send the same contents as before.

Besides what "actually" defines your response's contents, your application probably also considers "global" conditions, like which user is signed in:

class ApplicationController < ActionController::Base

  etag { current_user&.id }
  etag { current_user&.updated_at }


Under the hood, Rails generates an ETag header value like W/"f14ce3710a2a3187802cadc7e0c8ea99". In doing so, all objects from that etagge...

Git: Restore


git checkout is the swiss army of git commands. If you prefer a semantically more meaningful command for restoring tasks, use git restore instead.

With this command you can ...

  • ... do unstaging - git restore --staged
  • ... discard staged changes - git restore --staged --worktree
  • ... discard unstaged changes - git restore
  • ... restore deleted files - git restore
  • ... restore historic versions - git restore --source
  • ... recreate merge conflicts - git restore --merge
  • ... specifiy...

Git commands to discard local changes

Use case

You have uncommited changes (you can always check by using git status), which you want to discard.


Now there are several options to discard these depending on your exact situation.
The headlines will differentiate the cases whether the files are staged or unstaged.

Staged And Unstaged Changes

Revert all changes to modified files (tracked and untracked)

git reset --hard

If you might want to use the changes later on

git stash will add the changes to the stash, reverting the local repository to HE...

RubyMine: Find and Replace with Regex (Capture Groups and Backreferences)


In RubyMine you can use find and replace with capture groups (.*?) and backreferences $1 (if you have several groups: $[Capture-Group ID]).
Named captures (?<text>.*) are also supported.


Replace double quotes with single quotes

If you want to replace double quotes with single quotes, replacing every " with a ' is prone to errors. Regular expressions can help you out here.

  1. Open find and replace
  2. Activate the regex mode (click on the .* icon next to the "find" field).
  3. Fill in f...

Careful: `fresh_when last_modified: ...` without an object does not generate an E-Tag

To allow HTTP 304 responses, Rails offers the fresh_when method for controllers.

The most common way is to pass an ActiveRecord instance or scope, and fresh_when will set fitting E-Tag and Last-Modified headers for you. For scopes, an extra query is sent to the database.

fresh_when @users

If you do not want that magic to happen, e.g. because your scope is expens...

JSON APIs: Default design for common features

When you build a JSON API you need to come up with a style to represent attributes, pagination, errors or including associated objects. Instead of reinventing the wheel, you may reuse successful API designs.


JSON:API specifies common features found in most JSON APIs, like pagination, ordering and nested resources. The spec looks very similar to how one would build an API with Rails and uses similar patterns. Even if you don't plan on supporting the whole spec, it can still make sense to know how th...

Git: removing feature branches on merge

When working with feature branches, stale branches pile up over time. It's best to remove them right after merge, locally and on the remote, but it is a little tedious: you need to remember it, and perform the few steps manually each time.

Enter Git hooks. The folks at Liquid Light have built a little post-merge hook that will delete a feature branch on confirmation....

Rails: Fixing the memory leak / performance issues in prepend_view_path

Recently we detected a memory leak in one of our applications. Hunting it down, we found that the memory leak was located in Rails' #prepend_view_path. It occurs when the instance method prepend_view_path is called in each request, which is a common thing in a multi-tenant application.

On top of leaking memory, it also causes a performance hit, since templates rendered using the prepended view path will not be cached and compiled anew on each requqest.

This is not a new memory leak. It was [first reported in in 2014](https://github.com...

Debug file system access in a Rails application

It might sometimes be useful to check whether your Rails application accesses the file system unnecessarily, for example if your file system access is slow because it goes over the network.

The culprit might be a library like carrierwave that checks file existence or modification times, whereas your application could determine all this from your database.

Introducing strace

One option it to use strace for this, which logs all system calls performed by a process.

To do this, start your rails server using something like


Gem development: recommended gem metadata

The gemspec for gems allows to add metadata to your gem, some of which have a special meaning and are helpful for users.
You can provide links to your Github bugtracker or changelog file that are then used on the rubygems page of your gem (in the sidebar, e.g. see gem page of consul).

Here are some keys that should be filled:

Gem::Specification.new do |s|
  s.name = 'my-gem'
  s.homepage = 'https://github.com/makandra/my-gem'

  s.metadata = {
    'source_code_uri' => s.homepage,

Generating an Entity Relationship Diagram for your Rails application

This card explains how to generate an entity relationship diagram for your Rails application.
We also show how to limit your ERD to a subset of models, e.g. models inside a namespace.

Generating a full ERD

Option A: RubyMine

  1. Right-click anywhere in your project tree
  2. In the context menu, find the "Diagrams" menu item at/near the bottom
  3. Inside, choose "Show diagram" → "Rails Model Dependency Diagram"
  4. A new tab will open with the diagram inside. You can modify it there, and export it as an image.

Option B: Use rails-e...

PostgreSQL: "WHERE NOT <column> = '<value>'" statements do not include NULL values

Sometimes we write plain SQL queries in migrations so we don't have to mock ActiveRecord classes. These two migrations do the same:

class Migration1 < ActiveRecord::Migration[5.2]
  class User < ActiveRecord::Base; end

  def up
    add_column :users, :trashed, :boolean
    User.update_all(trashed: false)

class Migration2 < ActiveRecord::Migration[5.2]
  def up
    add_column :users, :trashed, :boolean

    update("UPDATE users SET trashed = #{quoted_false}")

The plain SQL migration is less code, but h...

Deployment: Merge consecutive commits without cherry-picking

You want to deploy new features but the latest commits are not ready for production? Then use git merge master~n to skip the n-last commits.


A big advantage of merging vs. cherry-picking is that cherry-picking will create copies of all picked commits. When you eventually do merge the branch after cherry-picking, you will have duplicate commit messages in your history.


It's time for a production deployment!

git log --pretty=format:"%h - %s" --reverse origin/production..origin/master

0e6ab39f - Feature A

Using ngrok for exposing your development server to the internet

Sometimes you need to access a dev server running on localhost from another machine that is not part of the same network. Maybe you want to use your phone to test a web page, but are only in a guest WiFi. In the past, we often used some port forwarding or other techniques to expose the service to the internet.

Enter ngrok, a command line tool that gives you an on-the-fly internet...

Rails 6.1: where.not changes behaviour from NOR to NAND

Since Rails 6.1, if we use where.not with multiple attributes, it applies logical NAND (NOT(A) OR NOT(B)) instead of NOR (NOT(A) AND NOT(B)). If you do not take care, this change will increase the matched set.


"Don't send newsletters neither to admins nor to trashed users!" becomes "Don't send newsletters to trashed admins".

User.where.not(role: 'admin', trashed: true)
# Before Rails 6.1, with NOR
=> "SELECT "users".* FROM "users" WHERE "users"."role" != 'admin' AND "users"."trashed" != TRUE"
# Equivale...