Unit Testing in Rails

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Unit Testing in Rails

• Testing Database Actions

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Testing the database

• Rails projects typically involve manipulating a
  database
• Testing with actual data, which you do not
  control, is infeasible
• There are likely legal issues as well
• You need to populate the test database with
  carefully designed data
• Creating the database with SQL each time is
  inefficient
• YAML provides a human-readable way of populating
  the test database
• Rails unit tests can be set to re-initialize the
  database for each test
• Some database tables might not be changed by
  testing
• The tests may involve only reading the database
• The database itself may be read-only
• Re-initializing the database for each test is
  slow and inefficient
• Rails unit tests can be set to not re-initialize
  the database for each test

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YAML

• YAML can be taken as an acronym for either
• Yet Another Markup Language
• YAML Aint Markup Language
• The purpose of YAML is to represent typical data
  types in human-readable notation
• Structure is indicated by indentation with
  spaces tabs are not allowed

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YAML example 1

• Rails uses YAML for configuring the database
• A typical entry in a .yml file would look like
  this
• development adapter mysql database
  cookbook host localhost username root
  password
• This describes the development database
• Each line in the above defines a key-value pair
• The values are strings they dont need to be
  quoted

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YAML example 2

• Rails also uses YAML for describing the contents
  of databases
• An example might look like this
• one id 1 category_id 1 title pizza
  description CB's favorite lunch date
  2007-05-09 instructions Phone pizza joint. Pay
  delivery guy. Chow down!two id 2
  category_id 2 title iced tea date
  2007-05-09
• The above example (adapted from
  http//www.oreillynet.com/lpt/a/7086) describes
  hashes one and two of simple values Strings,
  integers, dates
• Hashes can also be represented in brace notation
  name John Smith, age 33
• Other types of data can also be represented

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String literals

• String values do not need to be quoted
• Block literals (multiline strings) can be
  introduced with a pipe () or greater-than
  (gt) symbol
• The pipe preserves line ends and spacing
• street 123 Tornado Alley
  Suite 16
• The greater-than symbol allows text wrapping
• specialDelivery gt Follow the Yellow Brick
  Road to the Emerald City. Pay no attention
  to the man behind the curtain.

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Lists

• Lists are represented by single dashes (-)
• movies - Casablanca - North by Northwest
  - Notorious

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Casting

• YAML automatically detects simple types
• In the rare instances where casting is necessary,
  explicit casting can be performed with !!
• Examples
• a 123 an integer
• b "123" a string, disambiguated by
  quotes
• c 123.0 a float
• d !!float 123 also a float via explicit
  data type prefixed by (!!)
• e !!str 123 a string, disambiguated by
  explicit type
• f !!str Yes a string via explicit type
• g Yes a boolean True
• h Yes we have No bananas a string, "Yes" and
  "No"
  dismabiguated by context

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Creating a test database

• You can begin by using SQL to create an (empty)
  test database
• mysql -u root -p (When prompted
  for a password, just hit Enter) create
  database myApp_test grant all on
  MyApp_test. to 'ODBC'_at_'localhost' exit
• You can begin by giving commands to SQL to create
  a nonempty test database
• mysql MyApp_development ltcreate.sql
• (create.sql is a file containing the appropriate
  commands)

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Copying an existing database schema

• You can copy the database schema (not the actual
  records) from the development database to the
  test database
• rake dbtestclone_structure

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Creating a fixture file

• If you used scaffolding, you already have a file
  test/fixtures/table_name.ymlfor each table
  in your database schema
• Example
• Read about fixtures at http//ar.rubyonrails.org
  /classes/Fixtures.htmlyamlin5minutes id 1
  name Yaml in 5 minutes url http//yaml.kwiki.o
  rg/?YamlInFiveMinuteswikipedia id 2 name
  Wikipedia article on YAML url
  http//en.wikipedia.org/wiki/YAML
• If you don't have a YAML file already, you can
  create one in any text editor

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Creating test files

• If you used scaffolding, you already have a file
  test/unit/table_name.rbfor each table in
  your database schema
• Example
• require File.dirname(__FILE__)
  '/../test_helper'class RecipeTest lt
  TestUnitTestCase fixtures recipes
  Replace this with your real tests. def
  test_truth assert true endend
• If you don't have a unit test file already, you
  can create one in a text editor
• Note The keyword __FILE__ stands for the file
  this code is in
• test_helper is just a convenient place to put
  code used by many tests

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Creating tests

• The idea of a unit test is that you call a method
  (or methods) in the model, then specify what the
  result should be
• In ordinary unit tests, you test the return
  value of a method
• In database tests, you frequently have to access
  the database to get the result
• Your test methods must all begin with test_ and
  take no parameters
• Example def test_total_cost_of_order ... end
• If a method doesnt begin with test_, it wont be
  called automatically
• You then test the result with one or more of the
  various assert methods (see next slide)
• The unit test framework does all the rest of the
  work
• If your test methods modify the database, so that
  it should be reloaded after each test, use
• fixtures table_name

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Assertions

• assert(boolean, messagenil)
• assert_block(message"assert_block failed")
  ...
• assert_equal(expected, actual, messagenil)
• assert_in_delta(expected_float, actual_float,
  delta, message"")
• assert_instance_of(klass, object, message"")
• assert_kind_of(klass, object, message"")
• assert_match(regexp, string, message"")
• assert_nil(object, message"")
• assert_no_match(regexp, string, message"")
• assert_not_equal(expected, actual, messagenil)
• assert_not_nil(object, message"")
• assert_not_same(expected, actual, messagenil)
• assert_nothing_raised(args) ...
• assert_same(expected, actual, message"")
• flunk(message"flunked")
• Plus a few others....

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Useful methods I Creating and saving records

• Heres one way to create a record (in memory)
• my_record MyClass.newmy_record.col_1
  value_1my_record.col_2 value_2
• Heres an equivalent way
• my_record MyClass.new( col_1 gt value_1,
  col_2 gt value_2 )
• Heres how to save the newly created record
• my_record.save
• Heres how to create and save all in one go
• my_record MyClass.create( col_1 gt value_1,
  col_2 gt value_2 )
• Heres how to delete a record
• my_record.destroy
• Heres how to find out how many records are in
  the database
• n MyClass.count

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Useful methods I Reading records

• Here are some simple ways to get a record from
  the database
• my_record MyClass.find(first)
• Returns the first record in the database
• my_records MyClass.find(all)
• Returns an array of all the records in the
  database
• my_record MyClass.find(id)
• Returns a record with the given id
• my_records MyClass.find(id_1, id_2, ...)
• Returns an array of records with the given ids

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Useful methods II Reading records

• You wont find these methods in the Rails API,
  because they are generated, based on the column
  names in your table
• record MyClass.find_by_col_1(value_1)
• If col_1 is the name of a column in the database,
  this returns a record whose value in that column
  is value_1.
• record MyClass.find_all_by_col_1(value_1)
• If col_1 is the name of a column in the database,
  this returns an array of records whose value in
  that column is value_1.
• record MyClass.find_by_col_1_and_col_2(value_1,
  value_2)
• If col_1 and col_2 are the names of columns in
  the database, this returns a record whose value
  in col_1 is value_1 and whose value in col_2 is
  value_2.
• record MyClass.find_all_by_col_1_and_col_2(value
  _1, value_2)
• If col_1 and col_2 are the names of columns in
  the database, this returns an array of records
  whose value in col_1 is value_1 and whose value
  in col_2 is value_2.

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Useful methods III Updating records

• Heres how to update a record in the database
• my_record MyClass.find(id)my_record.col_2
  value_17my_record.save
• The save method uses the id field of the record
  to determine if the record already exists in the
  table
• If the record exists, it is updated
• If the record doesnt exist, it is created
• In fact, save just calls another method,
  create_or_update

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Example test method

• def test_create_and_destroy initial_rec_count
  Category.count new_rec Category.new
  new_rec.save assert_equal(initial_rec_count
  1, Category.count) new_rec.destroy
  assert_equal(initial_rec_count,
  Category.count)end

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The End