Here is a unit test for the stop()method to whet your appetite. We will be discussing some majorly used concepts here. The author selected the COVID-19 Relief Fund to receive a donation as part of the Write for DOnations program.. Introduction. Some basics of the mock library. Did February 2020 Have 28 Or 29 Days? What about if methods are with single prefix of underscore? These are usually bits of code that do things with the filesystem or involve network access. Python Unittest Example. The method … It can target a production test method and make it’s return value a MagicMock instance.. @patch is the same thing as using the MagicMock class. #5 Lastly here we set the value that we want the post method to return - the mocked HTTP response. Manually raising (throwing) an exception in Python. The library also provides a function, called patch(), which replaces the real objects in your code with Mock instances. In the unit tests, we use a wide variety of object-oriented concepts. Before diving into all the principles, heuristics and guidelines, let's see a representative unit test in action. In this Python Unittest tutorial, we will use the unittest module to demonstrate our examples to you. A professor I know is becoming head of department, do I send congratulations or condolences? A test method can be created by prefixing them with the test keyword. … And to create it, you must put it inside a class. import sys import unittest from unittest.mock import MagicMock, patch import foo class TestFoo(unittest.TestCase): @patch('cv2.imread') def test_load_image(self, imread): foo.load_image('test') assert imread.called Run it by executing: $ pytest test_foo.py. A class method is a method that’s shared among all objects. The result of that evaluation shadows your function definition. In the following example of Unittest in Python, we will take a simple function that calculates the modulus 3 of a value. You can use a classmethod with both objects and the class: The parameter name now belongs to the class, if you’d change the name by using an object it ignores that. Though a problem arises when you want to test the non-abstract methods of an abstract class. In der Software-Entwicklung werden oft Unittests durchgeführt, um einzelne Module eines Programmes auf Fehler zu überprüfen. Class methods can be can be called from instances and from the class itself. We use base class of unit test i.e. It allows automation, sharing of the setup and exit code for tests, and independent tests for every framework. To turn a method into a classmethod, add @classmethodbefore the method definition. The class method can then be used by the class itself. Imagine that when we wrote a Python class to extract some business places’ reviews with Google Place API, how could we ensure that we will extract the data correctly without sending requests to Google? (Or am I missing something here?). Then you can override a setUp() method to prepare a test fixture before each test and/or a classSetUp() class method to Create a Class. unittest.mock provides a core Mock class removing the need to create a host of stubs throughout your test suite. Try it Yourself » Create Object. exactly what I was looking for, should be the accepted answer. In this case, would it be best to test the private functions and not test the public run() function? A generator method / function is called to return the generator object. Thus, if you have a private method __A on MyClass, you would need to run it like so in your unit test: from unittest import TestCase class TestMyClass(TestCase): def test_private(self): expected = 'myexpectedresult' m = MyClass() actual = m._MyClass__A self.assertEqual(expected, actual) It allows you to replace parts of your system under test with mock objects and make assertions about how they have been used. ... One scenario is, the developer will implement same logic but move the code from one class to another, etc., and still keep the same business logic. python unittest tutorial. Unit tests are written to detect bugs early in the development of the application when bugs are less frequent and less expensive to fix. A class method is a method that is bound to a class rather than its object. Testsuite − It is used to club test cases together and execute them simultaneously. Assert that the value of result equals 6 by using the .assertEqual() method on the unittest.TestCase class; Defines a command-line entry point, which runs the unittest test-runner .main() If you’re unsure what self is or how .assertEqual() is defined, you can brush up on your object-oriented programming with Python 3 Object-Oriented Programming. In this case, we can use python module unittest to mock a requests.get and to test if we will get the expectant result. As expected, one test passed and one failed. assertFalse() is used to verify that the given condition is False or not. unittest.mock is a library for testing in Python. Ran 2 tests in 0.000s. As you test your Python code, there will be operations which are slow and painful to test. Here we extend the unit test class in the form of single inheritance. We use base class of unit test i.e. How to perform Automated Unit Testing with JavaScript? Or earlier. Difference between Agile Testing and Waterfall Testing. This post contains examples of how unittest test fixture functions and methods are written, and in what order they run. Knowing how to test private and protected methods is therefore useful, and the advice to skip doing so not great. First of all, you CAN access the "private" stuff, can't you? 33.1K views . Relevant/affected Python packages and their versions: unittest; Actual behavior. To create a class, use the keyword class: Example. Unit Testing is a one of the best practice that should be performed starting from the first stages and throughout the whole process of development. Sometimes we want to prepare a context for each test to be run under. To learn more, see our tips on writing great answers. Dadurch lassen sich Fehler deutlich leichter und schneller … There is another one called instance method but inner working of instance method is the same as the class method. How To Use unittest to Write a Test Case for a Function in Python Python. That’s why Python ships with unittest.mock, a powerful part of the standard library for stubbing dependencies and mocking side effects. Since I received a downvote for this answer, I'd like to point out that I had addressed the question as asked: "In this case, would it be best to test the private functions and not test the public run() function?". 25.3. unittest — Unit testing framework¶ (If you are already familiar with the basic concepts of testing, you might want to skip to the list of assert methods.). Both pytest and unittest offer just about any testing option you will ever need for most Python code. How do I unit test the methods in a method object? Let’s check out some exercises that will help understand Python’s .sort() method better. It may seem like a long post, but it’s mostly code examples and example output. If it is not installed in your system, use pip to install it. For Example, What Is The Date Three Days After Feb 27, 2020? ERROR – This indicates that the test raises an exception/error. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. These method names are not mangled, and that can be shown simply enough: Probably you should just test the run() method. unittest2 is a backport of Python 2.7’s unittest module which has an improved API and better assertions over the one available in previous versions of Python. Thus, if you have a private method __A on MyClass, you would need to run it like so in your unit test: The question came up about so-called 'protected' values that are demarcated by a single underscore. Python Unittest Examples: Mocking and Patching Last updated: 04 Jan 2020. All of these use the same method. However, my class looks like this: Essentially, I created a class for to process some input data through a pipeline of functions. What is the word for the imaginary line (or box) between the margin and body text of a printed page? Method & Description; 1: assertEqual(arg1, arg2, msg = None) Test that arg1 and arg2 are equal. What is the best way to do this? To call a class method, put the class as the first argument. 2: assertNotEqual(arg1, arg2, msg = None) The new features in unittest backported to Python 2.4+. “ TestCase ” to implement this operation. rev 2020.12.18.38240, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide. If you suspect or find problems, then you might want to switch to your debugger aspect and test the private methods. Catch multiple exceptions in one line (except block). 今回は、UnitTest でよく使われる setUp と tearDown について勉強しようと思う。 環境. A Python method is like a Python function, but it must be called on an object. Thanks for contributing an answer to Stack Overflow! Step 2 − Define a function to be tested. Unit testing is a software testing method by which individual units of source code, such as functions, methods, and class are tested, to establish if they are fit for use. You’ve proven that unittest is working, but look at what you had to do:. This module has several methods by which you can perform unittests. assertNotEqual ()- Tests that the two arguments are unequal in value. Created on Aug 19, 2018 @author: zhaosong ''' import unittest import HtmlTestRunner import xmlrunner class MyTestExample(unittest.TestCase): ''' This class demo how to setup test case and run test use python unittest module. This, along with its subclasses, will meet most Python mocking needs that you will face in your tests. Or earlier. The same pattern is repeated in many other languages, including C, Perl, Java, and Smalltalk. Making statements based on opinion; back them up with references or personal experience. It execute each test method defined inside the class and gives us the result. Uses of classmethod() classmethod() function is used in factory design patterns where we want to call many functions with the class name rather than object. In what way would invoking martial law help Trump overturn the election? It provides a class called TestCase, which you can derive your class from. How to verify an exception that has been thrown in unit testing C#? That is the main behavior of this module. A Class is like an object constructor, or a "blueprint" for creating objects. However, pytest has been written to have more streamlined code for testing than unittest. Step 4 − Define a test as a method inside the class. unittest - Automated testing framework. This module comes built-in with your Python 3+ installation, so there’s no need to install it using pip. FAIL – This indicates either test case has failed and an AssertionError exception is raised. The example below defines a class method. Actually, Python automatically maps an instance method call to a class method. It is the generator object that is then iterated over. It’s Not Feb 30. It allows you to replace parts of your system under test with mock objects and make assertions about how they have been used. Remember that the method name must start with test. A Python generator is a function or method that uses the yield statement to return a series of values when iterated over 1. 3. Mit diesem Modultest können Sie Ihren Code auf Fehler prüfen. How can massive forest burning be an entirely terrible thing? It mostly deals with controlling the speed of the car. Sort the list in ascending order with .sort() method. Example. Is it appropriate for me to write about the pandemic? Testrunner … Testsuite − It is used to club test cases together and execute them simultaneously. Clicking the Run Test overlay for a unit test method (within a unittest.TestCase class) leads to the test class setUp method being called, but not its setUpClass method; the setUpClass method only gets run if you click the Run Test overlay above the entire test class. Let's see the brief intro about each method that we are going to write. unittest.TestCase is used to create test cases by subclassing it. If there's a hole in Zvezda module, why didn't all the air onboard immediately escape into space? Python unittest.mock. It is involved in displaying the results after executing the tasks. Below is the project file structures in eclipse PyDev package explorer. from unittest.mock import patch def test_function_b (): # mock an object of class with patch. unittest.mock provides a way to mimic these bits of ‘slow’ code, so that your test suite can run fast, or to prevent you from having to write very complex tests. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. Testing Private Methods in Python (An Exception). The TestCase class of the Python Unittest library implements a list of assert methods. The unittest test framework is python’s xUnit style framework. Testcase − It is response specific base class in accordance with a given set of inputs. Most classes will have internal methods -- and it does not really matter in this case whether or not all the code in __A(), __B(), __C,() and __D() is actually in run() or not. Here we used to built-in methods like assertEqual() , assertTrue() & assertFalse(), assertEqual() is used to validate/compare the output with the result. unittest2 is a backport of the new features added to the unittest testing framework in Python 2.7 and onwards. The @classmethod Decorator: . In der Terminologie von C++ sind class members (inklusive der data member) normalerweise in Python public (Ausnahmen siehe Private Variablen) und alle member functions (Methoden) sind virtual. Who becomes the unlucky loser? With every method, we can specify a condition that must be true to continue executing the test. > python -m unittest -q test_lists in test_len - setUp() in test_len - test_len() in test_len - tearDown() in test_min - setUp() in test_min - test_min() in test_min - tearDown() ----- Ran 2 tests in 0.032s OK Note that the tests are wrapped with setUp() and tearDown() just as promised. Introduction. 3. Last Validated on September 30, 2020 Originally Published on September 30, 2020; The author selected the COVID-19 Relief Fund to receive a donation as part of the Write for DOnations program. They are useful for defining laying out the class interface, but deferring the implementation to the inherting classes. @patch can be used as a decorator for unittest methods. You can import the module by typing: import unittest Python unittest Methods. Python Unittest Assert Methods Now, let’s take a look at what methods we can call within Unit testing with Python: assertEqual ()- Tests that the two arguments are equal in value. These methods are optional. You were essentially suggesting he skips testing subroutines, though, or only test them manually. Unit Testing is the first level of software testing where the smallest testable parts of a software are tested. I'll get into the details later. Python How to assert a method is called in unit test using Mock/MagicMock Posted by All about Python on December 18, 2016. Calculate the centroid of a collection of complex numbers. Now in this Car class, we have five methods, namely, start(), halt(), drift(), speedup(), and turn(). The @classmethod decorator, is a built-in function decorator which is an expression that gets evaluated after your function is defined. The setUp method is run prior to each test in the class.tearDown is run at the end of every test. Unit Test with couple of functions. 2.Testing String Methods. Step 3 − Create a testcase by subclassing unittest.TestCase. Why is unappetizing food brought along to space? If you’re using an older version of Python, you’ll need to install the official backport of the library. Although it might look slightly weird in the beginning, .format() method is an extremely convenient method for string class objects. The unittest unit testing framework was originally inspired by JUnit and has a similar flavor as major unit testing frameworks in other languages. The above code is a short script to test 5 string methods. We can use the decorator @unittest.skip(). Sr.No. Python Classmethod. Introduction. How to deal with a situation where following the rules rewards the rule breakers. We shall see the output as. The output of the above code can be in three forms −, OK – This indicates that all tests generated have executed successfully. ask3m. Does Python have a ternary conditional operator? The unittest module comes with Python's standard library. The … Example. How digital identity protects your software. But you could always write a test function in MyClass if you have to test the internal stuff: Not the most elegant way to do it, to be sure, but it's only a few lines of code at the bottom of your class. Stack Overflow for Teams is a private, secure spot for you and Testrunner − It follows an outcome-based execution of tasks. Python's unittest module, sometimes referred to as 'PyUnit', is based on the XUnit framework design by Kent Beck and Erich Gamma. The following steps are involved in writing a simple unit test − Step 1 − Import the unittest module in your program. If the values do not compare equal, the test will fail. The Python standard library includes the unittest module to help you write and run tests for your Python code.. Tests written using the unittest module can help you find bugs in your programs, and prevent regressions from occurring as you change your code over time. In this article, we will learn about the fundamentals of software testing with the help of the unit test module available in Python 3.x. Unittest bei Python durchführen. site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. class TestFunctions(unittest.TestCase): Test methods. In this Python Programming Tutorial, we will be learning how to unit-test our code using the unittest module. Then you have to access them as BenDundee explains. unittest.mock provides a core Mock class removing the need to create a host of stubs throughout your test suite. It doesn't require creation of a class instance, much like staticmethod. (8 replies) Hello, I have a number of conceptually separate tests that nevertheless need a common, complicated and expensive setup. test_string_equality. Question: Write A Python Program And Also The Unittest Program For The Following Program Part 1: Date Arithmetic Operations Date_arithmetic()-> Tuple[datetime, Datetime, Int] Date Arithmetic Is Far More Difficult Than You Might Imagine. Usually Python comes with package unittest installed. You can vote up the ones you like or vote down the ones you don't like, and go to the original project or source file by following the links above each example. Why are Python's 'private' methods not actually private? In Python 3, up to and including 3.3, the control flow appears to have changed a bit: Python 3’s unittest package processes results after calling each test’s tearDown() method… this behavior can be confirmed if we simply add an extra line (or six) to our test class: Almost everything in Python is an object, with its properties and methods. Python's abstract base classes have at least one abstract method, so they cannot be instantiated directly. Python 3.x Anaconda Pycharm. pytest vs. unittest. Create a class named MyClass, with a property named x: class MyClass: x = 5. How can ultrasound hurt human ears if it is above audible range? By DavidMuller. Method 1 – No package available This is used to validate that each unit of the software performs as designed. This is not a good habit to adopt; unit tests should test as tight a sequence as possible, and your tests (unit and integration) should test with as much coverage as possible. This method tests whether two strings are equal or not using assertEqaul method of unittest.TestCase. The protocol method for iteration is __iter__(), so we can mock this using a MagicMock. unittest.mock provides a class called Mock which you will use to imitate real objects in your codebase.Mock offers incredible flexibility and insightful data. The unittest module can be used from the command line to run tests from modules, classes or even individual test methods: python -m unittest test_module1 test_module2 python -m unittest test_module.TestClass python -m unittest test_module.TestClass.test_method. The last block of the code at … Table of Contents ... from unittest.mock import patch from myproject.main import function_a def test_function_a (): # note that you must pass the name as it is imported on the application code with patch ("myproject.main.complex_function") as complex_function_mock: # we dont care what the return value … Assertions in Python Unittest Framework. As parameter the method always takes the class. The Python unit testing framework, sometimes referred to as “PyUnit,” is a Python language version of JUnit, by Kent Beck and Erich Gamma. Python is an object oriented programming language. Now lets a basic example to see how unit testing works. Python Unit Test with unittest. Unit Testing in Python Program using Unittest, Difference between Unit Testing and Integration Testing, Difference between Unit Testing and Sandwich Testing, Difference between Unit Testing and System Testing. Now, we are going to test different string methods with sample test cases. Any function that starts … your coworkers to find and share information. These methods are optional. How do I merge two dictionaries in a single expression in Python (taking union of dictionaries)? If you’re using PyCharm IDE, you can simply press ctrl+shift+F10 to run unittest module. If you don't set anything, the post method will return new Mock object on the fly. What does "steal my crown" mean in Kacey Musgraves's Butterflies? Note: The standard library includes unittest.mock in Python 3.3 and later. In this example, we put the pass statement in each of these, because we haven’t decided what to do yet. unittest.mock is a library for testing in Python. Categorical presentation of direct sums of vector spaces, versus tensor products, Obscure markings in BWV 814 I. Allemande, Bach, Henle edition. Test fixture − It serves as a baseline for the test cases in the associated environment. The Python unit testing framework, sometimes referred to as “PyUnit,” is a Python version of Java JUnit. How do I check whether a file exists without exceptions? Sometimes we want to prepare a context for each test to be run under. Python unittest Module. GitHub Gist: instantly share code, notes, and snippets. In this example the class method uses the class property name. @JavaSa I've updated the answer to answer that question. The following are 30 code examples for showing how to use unittest.TestCase().These examples are extracted from open source projects. In this case, I would need to initialize my class with the variables, call run, and test the outcome. Create Unit Tuple in Java using with() method. For example, let’s say you wanted to test the following method: Let’s call the drift() Python method on blackverna. The SelfDrivingCarclass is a partial implementation of the driving logic of a self-driving car. The syntax is: “{} {}”.format(value1, value2…) As curly brackets get replaced with values inside the parenthesis. A string 'contains ' substring method class TestFunctions ( unittest.TestCase ): # mock an object constructor, or class. S check out some exercises that will help understand Python ’ s why Python ships with unittest.mock a! Versions: unittest ; Actual behavior single inheritance can ultrasound hurt human ears if is. Used to club test cases in the associated environment ' methods not actually?! For example, add ( ) method example to see how unit testing frameworks in other languages slightly weird the. Problems, then you have to access them as BenDundee explains check whether a exists! Test private and protected methods is therefore useful, and whether or not on opinion ; back them up references! Value that we are going to test 5 string methods with sample test cases by subclassing.... Cases by subclassing it to access them as BenDundee explains are less frequent and less expensive fix! Drift ( ) function the post method to return the generator object is... 'S see the brief intro about each method that ’ s why ships... Box ) between the margin and body text of a value smallest testable parts of your system under test mock. Are Python 's standard library includes unittest.mock in Python 3.3 and later strings are equal testrunner − is! False or not it arrived at its destination a software are tested space. Stubbing dependencies and mocking side effects parts of your system under test with mock instances Date three Days after 27! Check out some exercises that will help understand Python ’ s no need to a. Discussing some majorly used concepts here referred to as “ dirty ” services into all the air immediately! Examples for showing python unittest class method to verify that the test will fail Days after Feb 27, 2020 removing the to... Case, we can use Python module unittest to mock a requests.get and to test outcome! Understand Python ’ s xUnit style framework method better new mock object on the fly (. Contributions licensed under cc by-sa and protected methods is therefore python unittest class method, and whether not. Functions and methods are written to detect bugs early in the beginning, (. Why did n't all the air onboard immediately escape into space them simultaneously test them manually get the result!: class MyClass: x = 5 and expensive setUp class, use pip to install it that things! Is response specific base class in accordance with a given set of inputs most Python mocking needs that you ever! In eclipse PyDev package explorer is True or not, what is the three... Union of dictionaries ) receive a donation as part of the new features to... Forms −, OK – this indicates either test case execution generated html report ``... The standard library includes unittest.mock in Python ( taking union of dictionaries ) actually, Python automatically maps instance. Skip doing so not great variables, call run, and a test method inside! Bugs early in the development of the setUp method is called in unit test for the (. 1 − import the unittest module to assert a method that ’ s no need to it. Text of a self-driving car one line ( or am I missing something here? ) provides. Case has failed and an AssertionError exception is raised the generator object run. Myclass: x = 5 donation as part of the library fixture functions and test. What does `` steal my crown '' mean in Kacey Musgraves 's Butterflies manually raising ( throwing ) exception... For DOnations program.. Introduction air onboard immediately escape into space it mostly deals with controlling the speed the... I test a private, secure spot for you and your coworkers to find and share information not! Passed and one failed the filesystem or involve network access throw an error clicking post! Step 2 − Define a function, called patch ( ) method is run the! Mocking side effects, should be the accepted answer to club test cases in the following example of in. Working, but look at what you had to do yet by clicking “ post your answer,. Write directly interacts with what we would label as “ dirty ” services an expression that gets evaluated your... Like staticmethod arg2 are equal or not situation where following the rules rewards the breakers. Variety of object-oriented concepts step in run ( each step in run ( each step == each function?... A professor I know is becoming head of department, do I test private! Import unittest Python unittest methods access the `` private '' stuff, ca n't you a that... When you want to test provides an easy way to introduce mocks into RSS. You were essentially suggesting he skips testing subroutines, though, or a class method called. With python unittest class method, a powerful part of the setUp method is an object constructor, or only test manually! With every method, so they can not be instantiated directly I test...: test methods code auf Fehler prüfen, Java, and a test to... Basic example to see how unit testing C #, mock would return instance of class! Nist want 112-bit security from 128-bit key size for lightweight cryptography or responding to other answers: test.... December 18, 2016 − import the unittest module in Python ( taking union of )! With patch as BenDundee explains unittest durchführen können, zeigen wir Ihnen in unserer Python-Anleitung write for DOnations..... Tests are written, and snippets and has a similar flavor as major unit testing in Python ( taking of... Driving logic of a class method is run at the end of every test learned... Your answer ”, you can simply press ctrl+shift+F10 to run unittest module method be! And Cisco ASR1000 face in your system under test with mock instances and not test the non-abstract methods of abstract... Receive a donation as part of the mock library implementation of the standard library includes unittest.mock in (! Arguments are unequal in value a testcase by subclassing it methods by which you can simply press ctrl+shift+F10 to unittest! Objects in front of it, you can import the unittest module in your code mock! – this indicates that all tests generated have executed successfully class from loses so many that! A heater python unittest class method Finding the right BFD timers between Juniper QFX5110 and Cisco ASR1000 are.., OK – this indicates that the given condition is False or not by prefixing them with the expected.! Modultest können Sie Ihren code auf Fehler zu überprüfen can simply press ctrl+shift+F10 to run module. The library 8 replies ) Hello, I would need to create host! Unittest Python unittest library python unittest class method a list of assert methods mock class removing the need to install.. 2 − Define a test method defined inside the class interface, but look at you... Article, we will get the expectant result will meet most Python mocking needs that you will need. Strings are equal or not using assertEqaul method of unittest.TestCase more, see our on. Ide, you can access the `` private '' stuff, ca n't you built-in with your Python,! Start with test 's Butterflies be created by prefixing them with the expected values answer! Will face in your system under test with mock objects and make assertions about how they been! Spot for you and your coworkers to find and share information it ’ s xUnit style framework as a inside. Number of conceptually separate tests that nevertheless need a common, complicated and expensive.. Airlines book you on other airlines if they cancel flights about unit works! Ll need to install it using pip instances and from the class itself what is the project file structures eclipse... Tests are written, and whether or not if I want to a... To introduce mocks into your RSS reader so there ’ s call the drift )! Can massive forest burning be an entirely terrible thing module comes with Python 's abstract base classes have least! Exit code for testing than unittest the development of the standard library for dependencies...: # mock an object constructor, or only test them manually generator /! T decided what to do: older version of Python, we will get expectant! Features added to the inherting classes have * to give up a house seat and electoral vote... Step 1 − import the unittest module comes with Python 's standard library for stubbing dependencies and side... ( arg1, arg2, msg = None ) test that arg1 and arg2 equal. Unittest testing framework was originally inspired by JUnit and has a similar flavor as major unit testing was... Sharing of the driving logic of a class rather than its object seat and electoral college?! This post contains examples of how unittest test framework is Python ’ call. Execute each test in the associated environment the unittest testing framework was inspired... Module unittest to mock a requests.get and to create it, you can simply ctrl+shift+F10... Be discussing some majorly used concepts here whether a file exists without exceptions it! Or responding to other answers unittest.TestCase is used to verify that the given condition is True not! Post contains examples of how unittest test framework is Python ’ s check out exercises! Require creation of a printed page by unittest supports fixtures, test suites, in. With Python 's 'private ' methods not actually python unittest class method answer to answer that question cookie policy inherting.. Not installed in your system, use the decorator @ unittest.skip ( < reason > ) exceptions in one (. Single prefix of underscore variety of object-oriented concepts arises when you want to test the outcome it using.!