Monday, March 23, 2020

The TDD Course for Beginners : Learn by Practicing 7 Katas

Learn how to do Test Driven Development using Ruby within 4 hours. You will get:

1. The transcript of the entire course in PDF.
2. TDD in Ruby ebook in PDF, Mobi and Epub formats
3. Members only TDD tutorial website that walks you through every exercise in the course.
4. Monthly Google hangout Q&A session that supports your learning objectives.
5. All the slides used in the course in PDF format.
6. TDD Course Tools Checklist for every sub-skill covered in the course.
7. TDD in Ruby Course Outline that was used to create the course.

How do I get access to the videos and all the above goodies?

For only $9 / month, you get my support and access to all of the above. Send me payment via Paypal to to get access today!


Jeff Casimir, Principal, Jumpstart Lab


The actual coding TDD examples for Fizz Buzz and Fibonacci were really well done
During the coding exercises the refactoring of code was a good illustration of how to improve certainty of test results
Good overview of the importance of testing
Each lecture / exercise was only 5-10 minutes providing nice incremental gains in the course


The instructor's delivery was not engaging - students tune out very quickly
First 61 minutes were very high level and included no actual coding
Instructors speaking voice was monotone and slow for the entire course no inflection, jokes, or anything to keep your attention
The audio between segments varied in quality to sometimes low quality not ideal for a $200 course
Instructor used whiteboard to write notes and diagram concepts during lecture (also wrote in cursive and at least 1 time wrote off viewable screen)


We wouldn't recommend it for Turing pre-requisite work, but could be valuable supporting material for students in the class.

Mylene Reiners

When you want a theoretical background on TDD, this course is great (and the Ruby part is not too hard for people knowing only a little Ruby...)

Yury Voloshin

This is a good introduction to TDD for those who either have never used it or who have a very rudimentary understanding of it. Some of the more advanced concepts toward the end are somewhat rushed through, but I' sure that can't be helped due to time constraints and to the nature of the material. At least now I know the topics that I need to into more deeply.


This course introduces a solid foundation for practicing TDD. The instructor definitely knows what he's teaching. Information is divided in small logical and understandable chunks/lectures.

Jesse Mignac

Techniques, examples and theoretical material. This course is a really nice start to TDD with Ruby

Andrew Platkin

Very good pace and learned alot

Thom Parkin

The beginning of this course seems a bit slow and very dry. But your patience is well rewarded because the depth and detail of information provided is priceless! Mr. Paranj uses a time-tested technique of methodical presentation of ideas, one built upon the other, to its ultimate success. I am grateful and impressed by this course.

Jikku Jose

I am very happy to have such a comprehensive course from Mr. Paranj. I have been trying to do TDD in my projects for quite sometime without much success. This course helped a lot to expose much of the concepts and details one should focus on while doing TDD.  I wish the examples mentioned in "Fake It till you make it" and "Triangulation" was a bit more involved rather than the basic ones presented so that the techniques could be better understood.  I thank Mr. Paranj and Udemy for the course, it really helped me. Hope more advanced Ruby related materials can be brought out.

Pawel Jackowski

Instructor knows TDD and explains it with ease. I am quite familiar with technique and just wanted to refresh knowledge and I still recommend course. I definitely learned something about common mistakes and importance of every step in TDD sequence. I enrolled for free.

Steve Freeman

Instructor uses katas very effectively to show the patterns behind TDD. His clear examples and pointers to material for further study were very helpful and I look forward to practicing katas on my own. If you're trying to make sense of TDD I highly recommend this class!

What are the requirements?

Basic programming skills
You need to have your favorite text editor installed on your machine
You need Ruby 2.0 or above installed on your machine.

What am I going to get from this course?

Do Problem Domain Analysis
Do Solution Domain Analysis
Design Test Cases
Write Tests First
Apply Canonical Test Structure when having difficulty in writing a test first.

Who is the target audience?

Beginners to Test Driven Development
You should already know how to write programs in Ruby
You should already know how to create an instance of a class and invoke methods.

Course Description

In this course you will learn the basics of Test Driven Development. You will learn how to do Problem Domain Analysis, Solution Domain Analysis, Designing Test Cases and Writing Tests First. Learn the Basics of Test Driven Development in Ruby using this Beginner Course. This course will take 4 hours to complete.

Practice skills using 7 katas

  • Use the downloadable checklists to guide you when coding
  • Learn 3 different techniques to do Test Driven Development
  • You can be more productive if you practice TDD at work. Companies that adopt Test Driven Development are great places to work.
The material used in this course is the result of feedback from students who attended my TDD bootcamps and tutorials. This is a course designed by a developer for developers.

The concepts are first explained in a presentation. Then a coding demo illustrates how to apply the theory in practice. At the end of the lesson an exercise is given to reinforce the material.

You will learn the following concepts:
  • Assertions
  • The structure of a test
  • TDD Cycle
  • Minimal Implementation
  • Starter Test
  • Story Test
  • Next Test
  • Refactoring
  • Obvious Implementation
  • Fake It Till You Make It
  • Triangulation
  • Hiding Implementation Details
You will be able to attend interviews for companies that demand TDD skills to get a six-figure salary. Complete with working files and code samples, you'll be able to work alongside the instructor and will receive a verifiable certificate of completion upon finishing the course. I have interviewed people and I have seen the common mistakes made by candidates.

Subscribe Now

For only $9 / month, you get my support and access to all of the above. Send me payment via Paypal to to get access today!

Monday, August 22, 2016

PHP print_r Equivalent in rails

In PHP you can print the human-readable information about a variable. In the views, the Rails equivalent is:

<%= debug obj %>
You can also use pretty print 'pp', in IRB:

require 'pp'

pp obj

In Rails console, you don't have to require 'pp'. The print method is used to inspect a variable. It will call the to_s method of an object. Doing:

print obj

is equivalent to:


class Demo
  def to_s
    "This is a demo"

d =

print d
This will print: "This is demo"

Thursday, August 18, 2016

rails generate model

  rails generate model NAME [field[:type][:index] field[:type][:index]] [options]

      [--skip-namespace], [--no-skip-namespace]  # Skip namespace (affects only isolated applications)
      [--force-plural], [--no-force-plural]      # Forces the use of the given model name
  -o, --orm=NAME                                 # ORM to be invoked
                                                 # Default: active_record

ActiveRecord options:
      [--migration], [--no-migration]        # Indicates when to generate migration
                                             # Default: true
      [--timestamps], [--no-timestamps]      # Indicates when to generate timestamps
                                             # Default: true
      [--parent=PARENT]                      # The parent class for the generated model
      [--indexes], [--no-indexes]            # Add indexes for references and belongs_to columns
                                             # Default: true
      [--primary-key-type=PRIMARY_KEY_TYPE]  # The type for primary key
  -t, [--test-framework=NAME]                # Test framework to be invoked
                                             # Default: test_unit

TestUnit options:
      [--fixture], [--no-fixture]   # Indicates when to generate fixture
                                    # Default: true
  -r, [--fixture-replacement=NAME]  # Fixture replacement to be invoked

Runtime options:
  -f, [--force]                    # Overwrite files that already exist
  -p, [--pretend], [--no-pretend]  # Run but do not make any changes
  -q, [--quiet], [--no-quiet]      # Suppress status output
  -s, [--skip], [--no-skip]        # Skip files that already exist

    Stubs out a new model. Pass the model name, either CamelCased or
    under_scored, and an optional list of attribute pairs as arguments.

    Attribute pairs are field:type arguments specifying the
    model's attributes. Timestamps are added by default, so you don't have to
    specify them by hand as 'created_at:datetime updated_at:datetime'.

    As a special case, specifying 'password:digest' will generate a
    password_digest field of string type, and configure your generated model and
    tests for use with Active Model has_secure_password (assuming the default ORM
    and test framework are being used).

    You don't have to think up every attribute up front, but it helps to
    sketch out a few so you can start working with the model immediately.

    This generator invokes your configured ORM and test framework, which
    defaults to Active Record and TestUnit.

    Finally, if --parent option is given, it's used as superclass of the
    created model. This allows you create Single Table Inheritance models.

    If you pass a namespaced model name (e.g. admin/account or Admin::Account)
    then the generator will create a module with a table_name_prefix method
    to prefix the model's table name with the module name (e.g. admin_accounts)

Available field types:

    Just after the field name you can specify a type like text or boolean.
    It will generate the column with the associated SQL type. For instance:

        `rails generate model post title:string body:text`

    will generate a title column with a varchar type and a body column with a text
    type. If no type is specified the string type will be used by default.
    You can use the following types:


    You can also consider `references` as a kind of type. For instance, if you run:

        `rails generate model photo title:string album:references`

    It will generate an `album_id` column. You should generate these kinds of fields when
    you will use a `belongs_to` association, for instance. `references` also supports
    polymorphism, you can enable polymorphism like this:

        `rails generate model product supplier:references{polymorphic}`

    For integer, string, text and binary fields, an integer in curly braces will
    be set as the limit:

        `rails generate model user pseudo:string{30}`

    For decimal, two integers separated by a comma in curly braces will be used
    for precision and scale:

        `rails generate model product 'price:decimal{10,2}'`

    You can add a `:uniq` or `:index` suffix for unique or standard indexes

        `rails generate model user pseudo:string:uniq`
        `rails generate model user pseudo:string:index`

    You can combine any single curly brace option with the index options:

        `rails generate model user username:string{30}:uniq`
        `rails generate model product supplier:references{polymorphic}:index`

    If you require a `password_digest` string column for use with
    has_secure_password, you can specify `password:digest`:

        `rails generate model user password:digest`

    If you require a `token` string column for use with
    has_secure_token, you can specify `auth_token:token`:

        `rails generate model user auth_token:token`

Here is the examples for using model generator in Rails 5:

    `rails generate model account`

        For Active Record and TestUnit it creates:

            Model:      app/models/account.rb
            Test:       test/models/account_test.rb
            Fixtures:   test/fixtures/accounts.yml
            Migration:  db/migrate/XXX_create_accounts.rb

    `rails generate model post title:string body:text published:boolean`

        Creates a Post model with a string title, text body, and published flag.

    `rails generate model admin/account`

        For Active Record and TestUnit it creates:

            Module:     app/models/admin.rb
            Model:      app/models/admin/account.rb
            Test:       test/models/admin/account_test.rb
            Fixtures:   test/fixtures/admin/accounts.yml
            Migration:  db/migrate/XXX_create_admin_accounts.rb

Manifest File

A manifest file contains metadata for a group of files that are part of a coherent unit. In Rails, app/assets/javascripts/application.js is a manifest file. In this case the metadata is the directives that include javascript libraries.

//= require jquery
//= require jquery_ujs
//= require_tree .

Monday, August 15, 2016

The Yo Yo Problem in Rails Source Code

This problem is prevalent in Rails framework. The super is used a lot that makes understanding the large framework code base difficult. You have to look up the hierarchy and consider the inherited behavior and state from the super classes.

Saturday, August 13, 2016

What is the difference between string and text types in rails migration?

The :string type is used for short text input such as text fields, drop downs, select boxes etc. The :text is used for long text such as text area.

How to rename a database column in Rails migration?

If you have not deployed the code to any environment, you can roll back the migration.

rake db:rollback

And create the migration with the right column by correcting the column name. If you have lot of data that you don't want to lose then renaming is the way to go.

Generate a new migration file for renaming the old column:

rails g migration RenameOldColumnToNewColumn
Then modify the change method in the generated migration file:

rename_column :table_name, :old_column, :new_column

rails generator for model with belongs_to

Comment belongs to a user.

rails g model comment content:text user:references

This command will automatically add the belongs_to in comment model. If you generate the model like this:

rails g model comment content:text user_id:integer

Rails will not add the belongs_to to the comment model. You have to do it manually.

How to run rails generate scaffold when the model already exists?

rails g scaffold article --skip

How to delete all data and recreate a database tables in Rails?

You can drop the database by:

rake db:drop
This will delete the database.

You can create the database by:

rake db:create
You can create all the tables in the database by:

rake db:migrate
You can combine all three commands database by:

rake db:drop db:create db:migrate
You can accomplish it with just one rake task by:

rake db:schema:load
This loads the schema.rb file into the database.

This rake task is dangerous. It is useful only in development environment only. Do not run in any other environment other than development.

Friday, August 12, 2016

How to get the Rails app root directory path in Rails console?

You can get the Rails app root directory path in Rails console like this:

rails c
Loading development environment (Rails 5.0.0)
>> Rails.root
=> #
>> Rails.root.class
=> Pathname

You can get any path in your Rails app by using join method:

>> Rails.root.join('app', 'assets')
=> #

You have to call to_s to get a string like this:

>> Rails.root.join('app', 'assets').to_s
=> "/Users/zepho/temp/zurb/app/assets"

How to roll back a migration file in Rails?

Rollback by Given Number of Steps

You can list all the rake tasks in Rails 5 by doing:

rake db -T | grep rollback
Rolls the schema back to the previous version (specify steps w/ STEP=n)

rake db:rollback           
This rollbacks by one version. You can use:

rake db:rollback  STEP=2
to revert the last two migrations and so on. 

Rollback to a Specific Version

Provide the version to db:migrate down:

rake db:migrate down VERSION=20160206120000
You can also go up to a given version:

rake db:migrate up VERSION=20160206120000

How to remove a column from a table in Rails console?

>> ActiveRecord::Migration.remove_column(:products, :price)
-- remove_column(:products, :price)
   (0.1ms)  begin transaction
   (0.7ms)  CREATE TEMPORARY TABLE "aproducts" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar, "price" decimal, "created_at" datetime NOT NULL, "updated_at" datetime NOT NULL)
   (0.4ms)  INSERT INTO "aproducts" ("id","name","price","created_at","updated_at")
                     SELECT "id","name","price","created_at","updated_at" FROM "products"
   (0.3ms)  DROP TABLE "products"
   (0.2ms)  CREATE TABLE "products" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "name" varchar, "created_at" datetime NOT NULL, "updated_at" datetime NOT NULL)
   (0.1ms)  INSERT INTO "products" ("id","name","created_at","updated_at")
                     SELECT "id","name","created_at","updated_at" FROM "aproducts"
   (0.2ms)  DROP TABLE "aproducts"
   (49.8ms)  commit transaction
   -> 0.0624s
=> []

You have to exit the Rails console and go into Rails console again:

rails c
Loading development environment (Rails 5.0.0)
>>{ |c| [, c.type]}
=> [["id", :integer], ["name", :string], ["created_at", :datetime], ["updated_at", :datetime]]

You can now see that the price column has been removed from the products table.

How to drop a table using Rails database migration in the console?

In Rails 5, you can go to the console and do this:

- drop_table(:products)
   (29.8ms)  DROP TABLE "products"
   -> 0.0303s
=> []
If you list the tables, you will see that products table is no longer in the database:

>> ActiveRecord::Base.connection.data_sources
=> ["schema_migrations", "ar_internal_metadata"]

How to list the tables and the table structure in Rails console?

In Rails 5:

The tables method has been deprecated:

DEPRECATION WARNING: #tables currently returns both tables and views. This behavior is deprecated and will be changed with Rails 5.1 to only return tables. Use #data_sources instead. (called from irb_binding at (irb):2)

So, you can list all the tables like this:

> ActiveRecord::Base.connection.data_sources
=> ["schema_migrations", "ar_internal_metadata", "products"]

You can then list the columns and it's type like this:{ |c| [, c.type]}
[["id", :integer], 
["name", :string], 
["price", :decimal], 
["created_at", :datetime], 
["updated_at", :datetime]]

How to get the current absolute URL in Rails

Absolute URL in Rails

In Rails 5, you can use:


Assuming, the request is:

get "/articles?page=2"

This will return:

This is defined in actionpack/lib/action_dispatch/http/request.rb.

Full path without the URL

For this request:

get "/articles"


will return:


For a request with params in the URL:

get "/articles?page=2"

It will return:


Undo Scaffolding in Rails

You can undo the scaffold command by using the destroy. You should also rollback the database transaction, if you have already run the migration generated by that scaffold.

rails destroy scaffold 'myscaffold'
rake db:rollback