TE3201 Schedule

Learning Outcomes

Testing

Quality Assurance → Testing →

What

Testing: Testing is operating a system or component under specified conditions, observing or recording the results, and making an evaluation of some aspect of the system or component. –- source: IEEE

When testing, we execute a set of test cases. A test case specifies how to perform a test. At a minimum, it specifies the input to the software under test (SUT) and the expected behavior.

📦 Example: A minimal test case for testing a browser:

Input – Start the browser using a blank page (vertical scrollbar disabled). Then, load longfile.html located in the test data folder.
Expected behavior – The scrollbar should be automatically enabled upon loading longfile.html.

Test cases can be determined based on the specification, reviewing similar existing systems, or comparing to the past behavior of the SUT.

A more elaborate test case can have other details such as those given below.

A unique identifier : e.g. TC0034-a
A descriptive name: e.g. vertical scrollbar activation for long web pages
Objectives: e.g. to check whether the vertical scrollbar is correctly activated when a long web page is loaded to the browser
Classification information: e.g. priority - medium, category - UI features
Cleanup, if any: e.g. empty the browser cache.

For each test case we do the following:

Feed the input to the SUT
Observe the actual output
Compare actual output with the expected output

A test case failure is a mismatch between the expected behavior and the actual behavior. A failure is caused by a defect (or a bug).

📦 Example: In the browser example above, a test case failure is implied if the scrollbar remains disabled after loading longfile.html. The defect/bug causing that failure could be an uninitialized variable.

Here is another definition of testing:

Software testing consists of the dynamic verification that a program provides expected behaviors on a finite set of test cases, suitably selected from the usually infinite execution domain. _{-– source: Software Engineering Book of Knowledge V3}

Some things to note (indicated by keywords in the above definition):

Dynamic: Testing involves executing the software. It is not by examining the code statically.
Finite: In most non-trivial cases there are potentially infinite test scenarios but resource constraints dictate that we can test only a finite number of scenarios.
Selected: In most cases it is not possible to test all scenarios. That means we need to select what scenarios to test.
Expected: Testing requires some knowledge of how the software is expected to behave.

Explain how the concepts of testing, test case, test failure, and defect are related to each other.

Quality Assurance → Testing → Test Automation →

What

An automated test case can be run programmatically and the result of the test case (pass or fail) is determined programmatically. Compared to manual testing, automated testing reduces the effort required to run tests repeatedly and increases precision of testing (because manual testing is susceptible to human errors).

Side readings:

[Quora post] What is the best way to avoid bugs
[Quora post] Is automated testing relevant to startups?

Quality Assurance → Testing → Test Automation →

Automated Testing of CLI Apps

A simple way to semi-automate testing of a CLI(Command Line Interface) app is by using input/output re-direction.

First, we feed the app with a sequence of test inputs that is stored in a file while redirecting the output to another file.
Next, we compare the actual output file with another file containing the expected output.

Let us assume we are testing a CLI app called AddressBook. Here are the detailed steps:

Store the test input in the text file input.txt.

add Valid Name p/12345 valid@email.butNoPrefix
add Valid Name 12345 e/valid@email.butPhonePrefixMissing

Store the output we expect from the SUT in another text file expected.txt.

Command: || [add Valid Name p/12345 valid@email.butNoPrefix]
Invalid command format: add 

Command: || [add Valid Name 12345 e/valid@email.butPhonePrefixMissing]
Invalid command format: add

Run the program as given below, which will redirect the text in input.txt as the input to AddressBook and similarly, will redirect the output of AddressBook to a text file output.txt. Note that this does not require any code changes to AddressBook.
```
java AddressBook < input.txt > output.txt
```
- 💡 The way to run a CLI program differs based on the language.
  e.g., In Python, assuming the code is in AddressBook.py file, use the command
  python AddressBook.py < input.txt > output.txt
- 💡 If you are using Windows, use a normal command window to run the app, not a Power Shell window.
A CLI program takes input from the keyboard and outputs to the console. That is because those two are default input and output streams, respectively. But you can change that behavior using < and > operators. For example, if you run AddressBook in a command window, the output will be shown in the console, but if you run it like this,
```
java AddressBook > output.txt 
```
the Operating System then creates a file output.txt and stores the output in that file instead of displaying it in the console. No file I/O coding is required. Similarly, adding < input.txt (or any other filename) makes the OS redirect the contents of the file as input to the program, as if the user typed the content of the file one line at a time.
📎 Resources:
- Using command redirection operators in Windows
Next, we compare output.txt with the expected.txt. This can be done using a utility such as Windows FC (i.e. File Compare) command, Unix diff command, or a GUI tool such as WinMerge.
```
FC output.txt expected.txt
```

Note that the above technique is only suitable when testing CLI apps, and only if the exact output can be predetermined. If the output varies from one run to the other (e.g. it contains a time stamp), this technique will not work. In those cases we need more sophisticated ways of automating tests.

CLI App: An application that has a Command Line Interface. i.e. user interacts with the app by typing in commands.

Quality Assurance → Testing → Regression Testing →

What

When we modify a system, the modification may result in some unintended and undesirable effects on the system. Such an effect is called a regression.

Regression testing is re-testing the software to detect regressions. Note that to detect regressions, we need to retest all related components, even if they were tested before.

Regression testing is more effective when it is done frequently, after each small change. However, doing so can be prohibitively expensive if testing is done manually. Hence, regression testing is more practical when it is automated.

Regression testing is the automated re-testing of a software after it has been modified.

a. True
b. False
c. Partially true

Explanation: Regression testing need not be automated but automation is highly recommended.

Explain why and when you would do regression testing in a software project.

Programing Basics

File Paths

A file has a filename and a path. The path specifies the location of a file on the computer, as a hierarchy of folders (also called directories).

📦 File C:\photos\2018\home.jpg

Filename: home.jpg
Path: C:\photos\2018 (Windows uses the back slash \ as the separator symbol in paths )
Folders in the path (C: is called the root folder):
```
C: {root}
  ˪ photos
      ˪ 2018
```

❗️ Windows file names and paths are not case sensitive: C:\photos\2018\home.jpg is same as C:\PHOTOS\2018\HOME.JPG.

📦 File /Users/john/home.jpg

Filename: home.jpg
Path: /Users/john (OS-X/Linux uses the forward slash / as the separator symbol in paths )
Folders in the path (the / at the start of the path is considered the root folder):
```
/ {root}
  ˪ Users
      ˪ john
```

❗️ OS-X/Linux file names and paths are case sensitive. /Users/john/home.jpg is NOT the same as /USERS/JOHN/HOME.JPG

The Python module os contains functions for dealing with files and folders. For example, you can use os.getcwd() to get the current working directory and os.chdir() to change the working directory to a different location.

📦

import os

cwd = os.getcwd() # store current working dir
print(cwd) # print current working dir
os.chdir('C:\\temp\\python') # change dir
print(os.getcwd()) # print current working dir
os.chdir(cwd) # change working dir back to original
print(os.getcwd())

→

C:\modules\te3201
C:\temp\python
C:\modules\te3201

💡 Note how the path 'C:\\temp\\python' uses double slash to escape the \. In OS-X or Linux, it can be something like /user/john/python (no need for double slash).

An escape sequence is a sequence of characters in a string literal that is taken together and interpreted in a special way. You can use an escape sequence to include a special character in a string literal without interpreting it as a special character. Given below are some examples:

Escape Sequence	Meaning	Example	Output
`\'`	single quote	`print('How\'s Life')`	`How's Life?`
`\"`	double quote	`print("Say \"wow\"")`	`Say "wow"`
`\\`	back slash	`print('files\\text')`	`files\text`

Another use of escape sequences is to give a special meaning to a character that normally does not have a special meaning. Here are some examples:

Escape Sequence	Meaning	Example	Output
`\t`	horizontal tab	`print('aaa\tbbb')`	`aaa` `bbb`
`\n`	line break	`print('hi\nthere!')`	`hi` `there!`

A path that specifies all folders starting from the root is an absolute path. A path that is specified relative to the current working directory is a relative path.

📦 Assume the current working directory is C:\modules\te3201 and you created a new folder inside it named exercises and put a ex.txt file in that folder.

Absolute path of the file: C:\modules\te3201\exercises\ex1.txt
Relative path of the file: exercises\ex1.txt

In a path, you can use the dot . as a shorthand to refer to the current working directory. Similarly, .. can be used to refer to the parent directory.

📦 If the current working directory is C:\modules\te3201, you can use any of the following to refer to C:\modules\te3201\exercises\ex1.txt.

exercises\ex1.txt
.\exercises\ex1.txt
..\te3201\exercises\ex1.txt
..\..\modules\te3201\exercises\ex1.txt

You can use os.mkdir() function to create folders and os.removedirs() to delete folders.

📦

print(os.getcwd())
os.makedirs('ex\\w1')
os.chdir('ex\\w1')
print(os.getcwd())
os.chdir('..') # go to parent dir
print(os.getcwd())
os.chdir('..')
os.removedirs('ex\\w1')

→

C:\repos\nus-te3201\sample-code
C:\repos\nus-te3201\sample-code\ex\w1
C:\repos\nus-te3201\sample-code\ex

os.path module has many functions that can help with paths. For example, os.paths.join() function can be used to generate file path that matches the current operating system.

📦 Consider the code below:

cwd = os.getcwd()
print(os.path.join(cwd, 'ex', 'w2'))

If you run it on a Windows computer in the folder C:\modules\te3201, it prints C:\modules\te3201\ex\w2.
If your run it on a OS-X computer in the folder /Users/john, it prints /Users/john/ex/w2.

❗️ To ensure that your code can work on any OS, you are advised to use os.path.join() function instead of hard-coding the path separators.

📦 contrasting hard-coding the separator vs using os.path.join():

❌ Works only on Windows	✅ Works on both Windows and OS-X
`os.makedirs('ex\\w1')`	`os.makedirs(os.path.join('ex', 'w1'))`

Exercise : Create Direcotry

Complete the functions given below, to behave as described by their docstrings, so that the code produces the given output.

import os

def create_dir(dir_name):
  """Create a directory dir_name in the current working directory
  
  Example:
  If the current directory is c:/foo/, create_dir('bar') creates 
  a c:/foo/bar directory.
  """
  pass # REPLACE WITH YOUR CODE HERE
  
  
def change_dir(relative_path):
  """Change to the directory dir_name relative to the current working directory
  
  Example:
  If the current directory is c:/foo/, change_dir('bar') changes 
  current working directory to c:/foo/bar
  """
  pass # REPLACE WITH YOUR CODE HERE
  
  
def print_current():
  """Print current working directory"""
  pass # REPLACE WITH YOUR CODE HERE 
  
  
def change_to_parent_dir():
  """Change to the parent directry of the current working directory
  
  Example:
  If the current directory is c:/foo/bar, change_to_parent_dir() changes 
  the working directory to c:/foo/
  """
  pass # REPLACE WITH YOUR CODE HERE
  
  
def check(dir_name):
  create_dir(dir_name)
  print_current()
  change_dir(dir_name)
  print_current()
  change_to_parent_dir()
  print_current()
  
check('foo')
check('bar')

⤵️ output when run in REPL.it

/home/runner
/home/runner/foo
/home/runner
/home/runner
/home/runner/bar
/home/runner

import os

def create_dir(dir_name):
  """Create a directory dir_name in the current working directory
  
  Example:
  If the current directory is c:/foo/, create_dir('bar') creates 
  a c:/foo/bar directory.
  """
  os.makedirs(dir_name)
  
  
...
  
  
def print_current():
  """Print current working directory"""
  print(os.getcwd())

Reading from Files

This section focuses on reading from text-based files (i.e., not binary files).

There are three steps to reading files in Python:

Call the open() function to receive a File object.
Call the read() method on the File object to receive file content.
Close the file by calling the close() method on the File object.

📦 The code below shows how to read from a text file.

file_path = os.path.join('data', 'items.txt')
f = open(file_path, 'r') # open in read mode
items = f.read()
print(items)
f.close()

→

Output (contents of the items.txt):

first line
second line
third line

💡 The 'r' argument in open(file_path, 'r') indicates that the file should be opened in read mode.

It is also possible to read the file content as a list of lines, using the readlines() method.

📦 The code below shows how to read file content as a list of lines.

f = open(file_path, 'r')
items = f.readlines()
print(items) # print as a list
for i in items: # print each item
  print(i.strip()) # use strip() to remove linebreak at the end of each line
f.close()

⤵️

['first line\n', 'second line\n', 'third line\n']
first line
second line
third line

💡 Note how each line ends with a \n which represents the line break. It can be removed using the strip() method.

Exercise : File Stats

Complete the functions given below, to behave as described by their docstrings, so that the code produces the given output.

def get_file_content_as_list(filename):
  """Return content of the file as a list of lines
  
  The file is expected to be in the current working directory.
  The lines in the list contains trailing line breaks.
  
  Example:
  If the a.txt has two lines 'aaa' and 'bbb', 
  get_file_content_as_list('a.txt') returns ['aaa\n', 'bbb']
  """
  return [] # REPLACE WITH YOUR CODE
  
def get_stats(contents):
  """Given a list of lines, return line count and letter count as a dictionary
  
  Trailing line breaks (if any) are not counted for letter count.
  Spaces, even trailing spaces, are counted for letter count.
  Example:
  get_stats(['aaa\n', 'bbb']) returns {'lines': 2, 'letters': 6}
  """
  stats = {}
  # ADD YOUR CODE HERE
  return stats
  
def analyze_file(filename): 
  contents_as_list = get_file_content_as_list(filename)
  print('lines in file:', contents_as_list)
  print('stats:', get_stats(contents_as_list))
  
analyze_file('file1.txt')
analyze_file('file2.txt')

file1.txt (2 lines, 22 letters):

aaa bbb ccc
ddd eee fff

file2.txt (4 lines, 10 letters -- note: the last line has a trailing space, which adds up to 10 letters):

a
bb
ccc
ddd

⤵️

lines in file: ['aaa bbb ccc\n', 'ddd eee fff']
stats: {'lines': 2, 'letters': 22}
lines in file: ['a\n', 'bb\n', 'ccc\n', 'ddd ']
stats: {'lines': 4, 'letters': 10}

strip() removes trailing line breaks but also trailing spaces. replace('\n', '') will remove the trailing line break but will keep the trailing spaces.

def get_file_content_as_list(filename):
  """Return content of the file as a list of lines
  
  The file is expected to be in the current working directory.
  The lines in the list contains trailing line breaks.
  
  Example:
  If the a.txt has two lines 'aaa' and 'bbb', 
  get_file_content_as_list('a.txt') returns ['aaa\n', 'bbb']
  """
  f = open(filename, 'r')
  lines = f.readlines()
  f.close()
  return lines

Writing to Files

Similar to reading from a file, writing to a file too is a three step process. One main difference is the file needs to be opened in write mode.

📦 The code below shows how to write to a text file.

file_path = os.path.join('data', 'items.txt')
f = open(file_path, 'w')  # open in write mode
f.write('first line\n')
f.write('second line\n')
f.close()

⤵️ contents of the items.txt:

first line
second line

💡 The 'w' argument indicates that the file should be opened in write mode.
💡 Unlike the print() function that prints content in a new line every time, the write function does not add an automatic line break at the end. You need to add a \n at each place you want a line break to appear in the file.

Opening a file in write mode and writing to it results in overwriting the content of the file contained before it was opened. To preserve original content and add to it, open the file in append mode.

📦 The code below shows how to append to a file.

f = open(file_path, 'a')  # open in append mode
f.write('third line\n')
f.close()

⤵️ contents of the items.txt:

first line
second line
third line

Exercise : Add Line Numbers

Complete the functions given below, to behave as described by their docstrings, so that the code produces the given output. Only one function needs to be modified.

def get_file_content_as_list(filename):
  """Return content of the file as a list of lines
  
  The file is expected to be in the current working directory.
  The lines in the list contains trailing line breaks.
  
  Example:
  If the a.txt has two lines 'aaa' and 'bbb', 
  get_file_content_as_list('a.txt') returns ['aaa\n', 'bbb']
  """
  f = open(filename, 'r')
  lines = f.readlines()
  f.close()
  return lines
  
def write_with_line_numbers(lines, filename):
  """Write the strings in lines to the file filename, after adding a line number to each line.
  
  Example:
  write_with_line_numbers(['aaa\n', 'bbb'], 'out.txt') writes the following content to out.txt
  1. aaa
  2. bbb
  """
  pass # REPLACE WITH YOUR CODE


def process_file(sourcefile, targetfile):
  """Copy the text in sourcefile to targetfile, but also add line numbers to each line.
  
  Example:
  Assume a.txt has the following text:
  aaa
  bbb
  process_file('a.txt', 'b.txt') results in b.txt having the following text:
  1. aaa
  2. bbb
  """
  contents = get_file_content_as_list(sourcefile)
  write_with_line_numbers(contents, targetfile)
  print(get_file_content_as_list(targetfile))
  
process_file('file1a.txt', 'file1b.txt')
process_file('file2a.txt', 'file2b.txt')

file1a.txt:

first line

second line
third line

file2a.txt:

hang in there

⤵️

['1. first line\n', '2. \n', '3. second line\n', '4. third line']
['1. hang in there']

def write_with_line_numbers(lines, filename):
  """Write the strings in lines to the file filename, after adding a line number to each line.
  
  Example:
  write_with_line_numbers(['aaa\n', 'bbb'], 'out.txt') writes the following content to out.txt
  1. aaa
  2. bbb
  """
  for n,line in enumerate(lines):
    f.write(str(n+1) ... ) # COMPLETE THIS LINE
  f.close()

CSV files

CSV files are often used as a simple way to save spreadsheet-like data. Each line in a CSV file represents a row in the spreadsheet, and commas separate the cells in the row. They usually have the .csv extension and can be opened in spreadsheet programs such as Excel or in any text editor.

📦 Here is the content of a simple CSV file (click here to download a copy) and how it looks like when opened in Excel.

4/11/2017,Alice Bee,4
5/11/2017,Chris Ding,12
5/11/2017,Brenda Chew,13
6/11/2017,Dan Pillai,5

→

💡 If a value itself contains a comma e.g., Foo, Emily, it can be enclosed in double quotes e.g., "Foo, Emily", to prevent it being misinterpreted as multiple values.

📦 This example shows how to use double quotes to handle commas inside a value:

7/11/2017,"Foo, Emily",5 interpreted as three values: 7/11/2017 and Foo, Emily and 5
7/11/2017,Foo, Emily,5 interpreted as four values: 7/11/2017 and Foo and Emily and 5

Although CSV files are text files that can be read/written using normal file access techniques covered earlier, Python has an in-built module named csv that provides functions to deal with CSV files more conveniently. For example, it provides a way to read a CSV file as a Reader object that knows how to interpret a CSV file.

📦 The code below shows how to use the csv module to read contents of a CSV file named deliveries.csv:

deliveries_file = open('deliveries.csv') # open file
deliveries_reader = csv.reader(deliveries_file) # create a Reader
for row in deliveries_reader: # access each line using the Reader
  print(row)
deliveries_file.close() # close file

⤵️

['4/11/2017', 'Alice Bee', '4']
['5/11/2017', 'Chris Ding', '12']
['5/11/2017', 'Brenda Chew', '13']
['6/11/2017', 'Dan Pillai', '5']

As you can see, Reader object returns content of a line as a list object with the value of each cell as an item in the list. Replacing the line,

...
print(row)
...

... with the following line,

...
print('Date:', row[0], '\tRecipient:', row[1], '\tQuantity:', row[2] )
...

... will give you the output shown below:

Date: 4/11/2017 	Recipient: Alice Bee 	Quantity: 4
Date: 5/11/2017 	Recipient: Chris Ding 	Quantity: 12
Date: 5/11/2017 	Recipient: Brenda Chew 	Quantity: 13
Date: 6/11/2017 	Recipient: Dan Pillai 	Quantity: 5

Note that all values read from a CSV files come as strings. If they are meant to represent other types, you need to convert the string to the correct type first.

📦 In this example the 3rd value of each row is converted to an int before adding them up.

deliveries_file = open('deliveries.csv') 
deliveries_reader = csv.reader(deliveries_file) 
total = 0
for row in deliveries_reader:
  # convert 3rd cell to an int and add to total
  total = total + int(row[2]) 

print('Total quantity delivered:', total)
deliveries_file.close()

⤵️

Total quantity delivered: 34

The csv module also provide an easy way to write to CSV files, one row at a time, using a Write object.

📦 The code below writes two rows to the pricelist.csv file.

output_file = open('pricelist.csv', 'w', newline='') # open file in write mode
output_writer = csv.writer(output_file) # get a Writer object
output_writer.writerow(['apples', '1', '1.5', 'True']) # write one row
output_writer.writerow(['bananas', '3', '2.0', 'False']) # write another row
output_file.close() # close file

The pricelist.csv file will now contain:

apples,1,1.5,True
bananas,3,2.0,False

💡 You can open a file in append mode if you want to append to it instead of overwriting current content.
e.g., output_file = open('pricelist.csv','a',newline='')
💡 The keyword argument newline='' need to be used when opening a CSV file in Windows. The reasoning behind it is beyond the scope of this book.

Exercise : Calculate GST

Suppose there is a CSV file in this format:

itemlist1.csv:

item,price
book,10.0
bag,50.0
"pens, pencils", 5.0

→

item	price
book	10.0
bag	50.0
pens, pencils	5.0

Write a program to calculate GST for each item at 7% and give the value as an additional column. The ouput should be in a new file.

updated_itemlist1.csv:

item,price,GST
book,10.0,0.7
bag,50.0,3.5
"pens, pencils", 5.0,0.35

→

item	price	GST
book	10.0	0.7
bag	50.0	3.5
pens, pencils	5.0	0.35

import csv

def calculate_GST(source_file, target_file):
  """Read the data from the CSV file source_file and write 
  the data, including the calculated GST values, to the CSV file target_file
  """
  input_lines = read_csv_lines(source_file)
  updated_lines = []
  
  # ADD YOUR CODE HERE
  
  write_to_csv_file(updated_lines, target_file)
   
  
def read_csv_lines(filename):
  """Return the values in the csv file (specified by the filename) as a list of lists
  each list representing a row of the file.
  
  Example: If the file file1.csv has the following contents,
  item,price
  book,10.0
  read_csv_lines('file1.csv') returns [['item', 'price']['book', '10.0']]
  
  """
  # return [] # REPLACE WITH YOUR CODE
  
  
def write_to_csv_file(lines, filename):
  """Write the given lines (a list of lists) to the CSV file (specified by filename)
  
  Example:
  write_to_csv_file([['item', 'price', 'GST']['book', '10.0', '0.7']], 'file2.txt')
  
  """
  pass # REPLACE WITH YOUR CODE
  

def process(source_file, target_file):
  
  calculate_GST(source_file, target_file)
  print(read_csv_lines(target_file))
  
  
process('itemlist1.csv', 'updated_itemlist1.csv')
process('itemlist2.csv', 'updated_itemlist2.csv')

🎯 At the end of this week you should be able to do something similar to the exercise given below (in your programming language/environment of choice):

Exercise from W8.2d:

Exercise : Calculate GST

Suppose there is a CSV file in this format:

itemlist1.csv:

item,price
book,10.0
bag,50.0
"pens, pencils", 5.0

→

item	price
book	10.0
bag	50.0
pens, pencils	5.0

Write a program to calculate GST for each item at 7% and give the value as an additional column. The ouput should be in a new file.

updated_itemlist1.csv:

item,price,GST
book,10.0,0.7
bag,50.0,3.5
"pens, pencils", 5.0,0.35

→

item	price	GST
book	10.0	0.7
bag	50.0	3.5
pens, pencils	5.0	0.35

import csv

def calculate_GST(source_file, target_file):
  """Read the data from the CSV file source_file and write 
  the data, including the calculated GST values, to the CSV file target_file
  """
  input_lines = read_csv_lines(source_file)
  updated_lines = []
  
  # ADD YOUR CODE HERE
  
  write_to_csv_file(updated_lines, target_file)
   
  
def read_csv_lines(filename):
  """Return the values in the csv file (specified by the filename) as a list of lists
  each list representing a row of the file.
  
  Example: If the file file1.csv has the following contents,
  item,price
  book,10.0
  read_csv_lines('file1.csv') returns [['item', 'price']['book', '10.0']]
  
  """
  # return [] # REPLACE WITH YOUR CODE
  
  
def write_to_csv_file(lines, filename):
  """Write the given lines (a list of lists) to the CSV file (specified by filename)
  
  Example:
  write_to_csv_file([['item', 'price', 'GST']['book', '10.0', '0.7']], 'file2.txt')
  
  """
  pass # REPLACE WITH YOUR CODE
  

def process(source_file, target_file):
  
  calculate_GST(source_file, target_file)
  print(read_csv_lines(target_file))
  
  
process('itemlist1.csv', 'updated_itemlist1.csv')
process('itemlist2.csv', 'updated_itemlist2.csv')

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