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Automating repetitive tasks with automated software testing gives the project  team , time to spend on more challenging and rewarding projects. Team members improve their skill sets and confidence and, in turn, pass those gains on to their organization.
Automating repetitive tasks with automated software testing gives the project  team , time to spend on more challenging and rewarding projects. Team members improve their skill sets and confidence and, in turn, pass those gains on to their organization.


== Creating A Migration ==
==Approaches to Test Automation==
<p>
<li>Code-driven testing: With the help of a variety of input arguments, the public (usually) interfaces to classes, modules or libraries are tested to validate that the results that are returned are correct.</li>
A migration is a sub class of ActiveRecord:: Migration which implements two methods: ‘up’ and ‘down’. The “up” method performs the required changes or transformations while the down methods reverses or roll backs them.</p><p>
<li>Graphical user interface testing: User interface events such as keystrokes and mouse clicks are generated by testing framework, and observes the changes that result in the user interface and validates whether the observable behavior of the program is correct or not.</li>
A migration can be created using the following command:
<pre>
rake generate migration CreateCourse
</pre>
Migration Created :
<pre>
class CreateCourse < ActiveRecord::Migration
def up
create_table :course do |t|
  t.string :name
  t.text :description
  t.timestamps
end
end
def down
drop_table :course
end
end
</pre>
The above migration CreateCourse has just been created, but has not been applied to the Database yet. This migration will add a table called courses with string column called name and the text column called description. A primary key column called id will also be created by default. The time stamp columns created_at and updated_at which ActiveRecord populates automatically will also be added. Reversing this migration is nothing but dropping the table.</p>
<p>
Migrations can also be used to fix bad data in the database or generate new fields.</p><p>
For Example:
<pre>
class AddGradesToStudents < ActiveRecord::Migration
def up
change_table :students do |t|
  t.boolean :receive_grade, :default => false
end
User.update_all ["receive_grade = ?", true]
end
def down
remove_column :students, :receive_grade
end
end
</pre>
The above migration adds receive_grades to the students table. We want the default value to be false for new students. But existing students are considered to have a grade, So we use the student model to set the flag to true for existing students.</p><p>


ActiveRecord<ref>http://api.rubyonrails.org/classes/ActiveRecord/Base.html</ref> provides methods that perform common data definition tasks in a database. A migration is like a Ruby class so you’re not limited to these functions. For example, after adding a column you can write a code to set the value of that column for existing records (if necessary using your models). The kind of object that  is yielded as a result of the migration code is object representing table.</p>
===Code-driven testing===
         
Code driven test automation is a key feature of agile software development, where it is known as test-driven development (TDD). Unit tests are written to define the functionality before the code is written. Only when all tests pass is the code considered complete. Proponents argue that it produces software that is both more reliable and less costly than code that is tested by manual exploration. It is considered more reliable because the code coverage is better, and because it is run constantly during development rather than once at the end of a waterfall development cycle. The developer discovers defects immediately upon making a change, when it is least expensive to fix. Finally, code refactoring is safer; transforming the code into a simpler form with less code duplication, but equivalent behavior, is much less likely to introduce new defects.
== Updating Migrations ==
<p>
If you wish to make changes to the migration and you have already run the migration then you cannot just edit the migration and run it again. Rails will consider it has already run the migration, so it will do nothing on running “rake db:migrate”. The migration has to be rolled back and then make changes to the migration and run it.
It is not recommended to edit existing migration and that too if it has been run on production systems. Instead, writing a new migration that performs the changes required is better. Making changes to a newly generated migration that has not been committed to source code is relatively safe.</p><p>
Migrations are stored as files in the db/migrate directory, for every migration class. The name of the file is of the form YYYYMMDDHHMMSS_create_course.rb, that is nothing but a UTC timestamp identifying the migration followed by an underscore followed by the name of the migration.
</p>


== Anatomy of Migrations ==
===Graphical User Interface (GUI) testing===
<p>
<p>A variation on this type of tool is for testing of web sites. Here, web page is the “interface”. Such a framework utilizes entirely different techniques because it is reading HTML instead of observing window events. Another variation is scriptless test automation that does not use record and playback, but instead builds a model of the Application Under Test (AUT) and then enables the tester to create test cases by simply editing the test parameters and conditions. Test-case maintenance is  easy, as there is no code to maintain .As the AUT changes the software objects can simply be re-learned or added. It can be applied to any GUI-based software application. The problem with this model is that  AUT is actually implemented using test scripts, which have to be constantly maintained whenever there's change to the AUT.</p>
Migrations are a subclass of the Rails class ActiveRecord::Migration. The class must contain at least two methods i.e up and down.
<pre>
class CreateCourses < ActiveRecord::Migration
def self.up
#...
end
def self.down
#...
end
end
</pre>
The ‘up’ method used to apply schema changes for this migration and the ‘down’ method is used to undo the changes. Example: the ‘up’ method creates a table with all the attribute description for the migration whereas the ‘down’ method can be used to drop the table for the same migration.
<pre>
Class CreateCourses < ActiveRecord::Migration
def self.up
      add_column :room_no, :integer
end
def self.down
      remove_column :room_no
end
end
</pre>
</p>


== Relationship between Model and Migration ==
In Rails, a model<ref>http://www.tutorialspoint.com/ruby-on-rails/rails-active-records.htm</ref> internally maps itself to a database table. The table in the database must be the plural form of the model’s class. If we generate a model called Course, Rails automatically looks for a table called courses in the database.
You can use the Rails generator to generate both the model and a corresponding migration using the following commands:
<pre>
rake generate model Course name: string description: text
</pre>
will create a migration that looks like this
<pre>
class CreateCourses < ActiveRecord::Migration
def change
  create_table :courses do |t|
t.string :name
t.text :description
t.timestamps
  end
end
end
</pre>


== Creating a Standalone Migration ==
== Creating a Standalone Migration ==

Revision as of 00:50, 27 October 2012

Automated Testing

Every software development group tests its products but still defects are always present in delivered software. Test engineerings always try to catch these errors but they always creep in and they often reappear, even with the best manual testing processes. Automated software testing is the best way to increase the effectiveness, efficiency and coverage of software testing. Automation Testing is the use of software to control the execution of tests, the comparison of actual outcomes to predicted outcomes, the setting up of test preconditions, test design, and other test control and test reporting functions. usually, test automation involves automating a manual process already in existence that uses a formalized testing process. There are many tools available to perform automation testing today.

Manual Testing

Manual testing is the method in which testing of the software is done manually. In this type of testing, a tester acts like an end-user. All features of a software are tested to know if the behavior of the software is exactly according to the expectations of the customer. The tester uses a test plan. Other than test plan, there are test cases written, which are used for implementing the test plan. Although manual tests may find many defects in a software application, it is a laborious and time consuming process. In addition, it may not be effective in finding certain classes of defects.

Why Automation Testing

Automated software testing has long been considered critical for big software development organizations but is often thought to be too expensive or difficult for smaller companies to implement. Many companies are recognizing the importance of automating the work of testers and including the auto-test as part of the regular build process. The results of the automatic test are seen as a measure of the current quality of the software. Combined with a code coverage tool it gives the answer to the all-elusive question: "How much of my code is currently running ok?."

The below factors make automation testing important:

Automated Testing is both Time and Money Saving

During software development cycle, software tests have to be repeated very often to ensure quality. Software tests need to be repeated, every time a change in the source code happens. For each release of the software it may be tested on all supported operating systems and hardware configurations. Repeating these tests manually is costly and time consuming. Once created, automated tests can be run over and over again at no additional cost and they are much faster than manual tests. The time to run these repetitive tests is reduced from days to hours by automated software testing. Saving the time directly translates into cost savings.

Improves Accuracy

Manual testers are bound to make mistakes during monotonous manual testing. With Automated tests, the probability of errors occuring is relatively low. Automated tests perform the same steps precisely every time they are executed and never forget to record detailed results.

Increases Test Coverage

Automated software testing can increase the depth and scope of tests to help improve software quality. Lengthy tests that are difficult to be conducted manually can be run unattended in Automation testing. They can even be run on multiple computers with different configurations. Automated software tests can easily execute thousands of different complex test cases during every test run providing test coverage that is impossible with manual tests.

Automated Software Testing Does What Manual Testing Cannot

A controlled web application test with thousands of users cannot be performed by even the largest software departments. Automated testing can simulate tens, hundreds or thousands of virtual users interacting with network or web software and applications.

Helps Developers and Testers

Shared automated tests can be used by developers to find problems quickly before sending the code for Quality assurance. Tests would run automatically whenever source code changes are checked in and in case of failure error reports would be automatically sent to the team or the developer. Features like these save developers time and increase their confidence.

Improves Team Morale

Automating repetitive tasks with automated software testing gives the project team , time to spend on more challenging and rewarding projects. Team members improve their skill sets and confidence and, in turn, pass those gains on to their organization.

Approaches to Test Automation

  • Code-driven testing: With the help of a variety of input arguments, the public (usually) interfaces to classes, modules or libraries are tested to validate that the results that are returned are correct.
  • Graphical user interface testing: User interface events such as keystrokes and mouse clicks are generated by testing framework, and observes the changes that result in the user interface and validates whether the observable behavior of the program is correct or not.

    • Code-driven testing

    Code driven test automation is a key feature of agile software development, where it is known as test-driven development (TDD). Unit tests are written to define the functionality before the code is written. Only when all tests pass is the code considered complete. Proponents argue that it produces software that is both more reliable and less costly than code that is tested by manual exploration. It is considered more reliable because the code coverage is better, and because it is run constantly during development rather than once at the end of a waterfall development cycle. The developer discovers defects immediately upon making a change, when it is least expensive to fix. Finally, code refactoring is safer; transforming the code into a simpler form with less code duplication, but equivalent behavior, is much less likely to introduce new defects.

    Graphical User Interface (GUI) testing

    A variation on this type of tool is for testing of web sites. Here, web page is the “interface”. Such a framework utilizes entirely different techniques because it is reading HTML instead of observing window events. Another variation is scriptless test automation that does not use record and playback, but instead builds a model of the Application Under Test (AUT) and then enables the tester to create test cases by simply editing the test parameters and conditions. Test-case maintenance is easy, as there is no code to maintain .As the AUT changes the software objects can simply be re-learned or added. It can be applied to any GUI-based software application. The problem with this model is that AUT is actually implemented using test scripts, which have to be constantly maintained whenever there's change to the AUT.


    Creating a Standalone Migration

    If you are creating migrations for other purposes, then a migration generator is used: 

    $ rails generate migration AddSemesterToCourse

    This will create an empty but appropriately named migration: 

    class AddPartNumberToProducts < ActiveRecord::Migration
def change
end
end

    Applying Migration to Development

    Since CreateCourse migration has been created but not applied to the database, the following command is used to apply the migration to the development database: 

    rake  db:migrate

    Every Rails Database has a table called schema_migrations maintained by the migration code. Whenever a migration is applied successfully a new row will be added to schema_migrations table. The schema_migrations table has a version column. When you run rake db:migrate, the task first looks for the schema_migrations table. It will be created if it does not exist. The migration code then looks at all the migration files in db/migrate and skips from considering any that have a version number that is already in the database. It then continues by applying the remaining migrations in turn creating a new row in the schema_migrations table for every migration.

    Applying Migration to Production

    The following command is used to apply migration to the production database: 

    heroku rake db:migrate

    In the above example the production database is Heroku.

    Running Specific Migrations

    If you need to run a specific migration up or down, the db:migrate:up and db:migrate:downtasks will do that on including the version also.

    For example, 

    rake db:migrate:up VERSION=20080906120000

    The above command will run the up method from the 20080906120000 migration. These tasks still check whether the migration has already run, so for example db:migrate:up VERSION=20080906120000 will do nothing if Active Record believes that 20080906120000 has already been run.

    Rolling Back a Migration

    The following command is used to rollback the last migration: 

    rake db:rollback

    Rollback is performed when you made some mistake and instead of tracking down the version number of the previous migration, you can just rollback and run it after making changes.

    If you need to rollback several migrations, a STEP parameter is used. For example, 

    rake db:rollback STEP=2

    The above command will rollback the last 2 migrations. The db:migrate:redo task is an easy way for doing a rollback and then migrating again. If you need to redo several migrations, a STEP parameter is used. For example, in order to redo the last 4 migrations, the command is 

    rake db:migrate:redo STEP=4

    “rake db:reset” is the command for resetting the database. This will drop the databse, recreate it and loads the current schema into it.

    Problems with Migration

    One major problem Migrations suffer is that most databases do not support the rolling back of create table or alter table i.e. DDL statements in general. Let’s consider an example where a migration tries to create two tables. 

    class Example < ActiveRecord::Migration
	def self.up
   	create_table :first do ...
	  
   	end
	   create_table
:second do ...
	
	   end
	end
	def self.down
   	drop_table :second
   	drop_table :first
	end
end

    In the above example the up method is used for creating the tables first and second and the down method is used to dropping the tables. Now, consider a situation where there is a problem creating the second table. Then the database will contain only the first table and not the second table. So if you try to rollback the migration, it won’t work as the original migration failed and the schema version in the database wasn’t updated. So you cannot roll back it. One solution to the above problem is, to manually change the schema information and drop the table first. But, it is recommended in these cases to simply drop the whole database, create the whole thing again and apply migrations to bring it back to the original state.

    Advantages of Migration

    1. You can identify each migration and know when it has taken place.
    2. Some migrations can also be rolled back. We can specify what the roll back procedure is.
    3. Migrations can be managed with version control.
    4. Automation – Automate things to be done which makes it reliably repeatable. For example, In Ruby on Rails, we use Bundler instead of installing all gems manually. In short, specify what needs to be done and automate it.

    Disadvantages of Migration

    1. One drawback of Rails migrations is that all migrations occur at the database level, not the table level.
    2. The whole discussion about Migration suggest that they are dangerous to use on production database. One should backup the database first and then use migrations on the production database.
    3. Most databases do not prop up the rolling back of data definition language(DDL)<ref>http://en.wikipedia.org/wiki/Data_definition_language</ref> statements.

    Conclusion

    In a nutshell, Database Migration is a very efficient way to handle the discrepancies that occur between databases. i.e. changes made in one database not reflecting in other. It is a convenient way to alter the database in structured and organized manner. Rails migrations are mostly similar to version control of databases. Rails migrations are database independent but SQL scripts are not.

    References

    <references/>

    Additional Reading

    1. http://guides.rubyonrails.org/migrations.html#anatomy-of-a-migration
    2. http://www.ibm.com/developerworks/java/library/j-cb08156/index.html
    3. http://jacqueschirag.wordpress.com/2007/08/12/rants-about-rails-database-migrations
    4. http://www.oracle.com/technetwork/articles/kern-rails-migrations-100756.html
    5. Agile Web Development With Rails, Fourth Edition, Sam Rooby, Dave Thomas, David Heinemeier Hansson.
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