What are the main advantages and disadvantages of writing unit tests?

Main advantages of unit tests:

• Early detection of errors — tests check individual components, allowing quick identification and fixing of bugs.
• Simplification of refactoring — having tests ensures that code changes do not break existing functionality.
• Code documentation — tests demonstrate how a module should work.
• Automation of verification — tests can be run automatically during project build.

Disadvantages of unit tests:

• Time costs for writing and maintenance — especially with frequent requirement changes.
• Do not cover integration and system errors — only test individual modules.
• Can be fragile — if tests are too tightly coupled with implementation, they break with minor changes.

In iOS development, unit tests are usually written using XCTest. For example, a test for checking a method:

func testSum() {
    let calculator = Calculator()
    XCTAssertEqual(calculator.sum(2, 3), 5)
}

Thus, unit tests are an important tool for improving code quality but require a reasonable approach to their writing and maintenance.