Difference between End-to-end Testing and Unit Testing

1. End-to-end Testing:
End-to-end testing is the type of software testing used to test entire software from starting to the end along with its integration with the external interfaces. The main purpose of end-to-end testing is to identify the system dependencies and to make sure that the data integrity and communication with other systems, interfaces, and databases to exercise complete productions. 

Advantages of End-to-End Testing :

• Comprehensive Testing: End-to-end testing ensures that all components of an application work together as expected, thereby providing comprehensive testing coverage.
• Realistic Scenarios: This type of testing simulates realistic process, which helps to identify issues that may not be detected in other forms of testing.
• Customer-Centric Testing: End-to-end testing focuses on the user’s experience, and ensures that the application meets the customer’s requirements.
• Early Bug Detection: By testing the entire system, including all its components, end-to-end testing helps detect bugs and defects early in the software development lifecycle.
• Streamlined Testing Process: End-to-end testing reduces the time and effort required to perform separate unit tests, integration tests, and system tests.

Disadvantages of End-to-End Testing :

• Time-Consuming: End-to-end testing is often time-consuming due to the complexity of the test scenarios, and may require significant resources.
• Costly: This type of testing can be expensive, as it involves testing the entire system, which may require a significant investment in time, personnel, and infrastructure.
• Limited Test Coverage: End-to-end testing may not cover all scenarios, as it is impossible to test every possible combination of inputs, especially in large systems.
• Difficult to Isolate Issues: When a test fails, it can be difficult to isolate the cause of the failure, as it may be due to issues in multiple components.
• Maintenance: End-to-end tests are often fragile and require frequent updates as the application evolves, leading to additional maintenance costs.

2. Unit Testing:
Unit Testing is the type of software testing level in which each individual component of software are tested separately. It is generally performed by a developer. It can’t be used for those systems which have a lot of interdependence between different modules. It does not allow for parallel testing. 

Advantages of Unit Testing :

• Early Bug Detection: Unit tests detect bugs early in the development cycle when they are easier and less costly to fix. Since each unit is tested in isolation, it is easier to identify and isolate issues.
• Increased Quality of Code: Unit tests ensure that each unit or component works as expected and meets the requirements, leading to higher code quality and more reliable software.
• Faster Feedback: Unit testing provides fast feedback to developers, allowing them to quickly identify and fix issues, reducing the overall development time.
• Cost-effective: Unit testing is a cost-effective testing approach as it requires fewer resources compared to other types of testing, such as end-to-end testing or integration testing.
• Simplified Debugging: Since each unit is tested in isolation, debugging is easier and less time-consuming, as developers can quickly identify the cause of the problem.

Disadvantages of Unit Testing :

• Limited Scope: Unit testing only tests individual units in isolation, and it may not capture the interactions and dependencies between the units, which can lead to issues in the integrated system.
• Time-consuming: Writing and maintaining unit tests can be time-consuming, especially for complex systems with many units.
• Skill Required: Writing effective unit tests requires a certain level of skill and experience in software testing, which may not be present in every developer.
• False Sense of Security: Unit tests only test individual units and do not guarantee that the system will work correctly as a whole.
• Overhead: Maintaining a comprehensive suite of unit tests can create additional overhead, which can be burdensome, particularly in large and complex systems.
  

Difference between End-to-end Testing and Unit Testing :

S. No.	End-to-end Testing	Unit Testing
1.	In end-to-end testing, the behavioral flow of the software is tested.	Unit testing generally focuses on functional verification.
2.	It tests the software system and the connected systems both combine.	In unit testing, software’s module are tested separately.
3.	It is generally performed manually.	It is performed both manually and automated.
4.	The Quality Assurance team conducts end-to-end tests.	Developers conduct unit tests.
5.	Requirement of more hardware resources and database access and other external dependencies are also needed for end-to-end tests.	The execution of individual unit tests is possible from the command line and therefore, you are able to run a small number that are pertinent to your work.
6.	End-to-end testing is not cost efficient.	Unit testing is cost efficient.
7.	End-to-end testing is performed for all testing processes at end.	Unit testing is performed for testing processes first.
8.	Defects are not identified easily in end-to-end testing.	Defects are identified easily in unit testing.
9.	Flow from end-to-end is tested.	Unit testing comprise of independent modules.
10.	Knowledge about interconnected systems is required.	Knowledge of interconnected systems is not required.
11.	Comparatively less execution speed than unit testing.	Execution speed is fast in comparison to End-to-end Testing.
12.	A lot of effort is required to write and maintain and time taken relies on complexity level of the application and number of test cases required to execute.	Less effort is required to write and maintain if TDD approach is followed.
13.	End-to-end tests are black-box.	Unit tests are white-box.
14.	The test environment is used to execute End-to-end tests.	Developer’s machine is used to execute unit tests.
15.	End-to-end tests must be run sequentially.	Unit tests can be run in parallel.