Make sure that include unit test case box is checked when creating a new project as shown below:

• Import the class, which contains the method to be tested.
• Perform the operation with dummy data.
• Now compare the result of operation with expected result.

- (void)testReverseString{
NSString *originalString = @"hi_my_name_is_siddharth";
NSString *reversedString = [self.someObject reverseString:originalString];
NSString *expectedReversedString = @"htrahddis_si_eman_ym_ih";
XCTAssertEqualObjects(expectedReversedString, reversedString, @"The reversed string did not match the expected reverse");
}

Feed the dummy data to the method under test if required & then compare the expected & actual results.

- (void)testDoSomethingThatTakesSomeTime{
XCTestExpectation *completionExpectation = [self expectationWithDescription:@"Long method"];
[self.someObject doSomethingThatTakesSomeTimesWithCompletionBlock:^(NSString *result) {
    XCTAssertEqualObjects(@"result", result, @"Result was not correct!");
    [completionExpectation fulfill];
}];
[self waitForExpectationsWithTimeout:5.0 handler:nil];
}

• Feed the dummy data to the method under test if required.
• The test will pause here, running the run loop, until the timeout is hit or all expectations are fulfilled.
• Timeout is the expected time for the asynchronous block to response.

1. For Synchronous methods :

- (void)testPerformanceReverseString {
    NSString *originalString = @"hi_my_name_is_siddharth";
    [self measureBlock:^{
        [self.someObject reverseString:originalString];
    }];
}

2. For Asynchronous methods :

- (void)testPerformanceOfAsynchronousBlock {
   [self measureMetrics:@[XCTPerformanceMetric_WallClockTime] automaticallyStartMeasuring:YES forBlock:^{
    
    XCTestExpectation *expectation = [self expectationWithDescription:@"performanceTestWithResponse"];
    
    [self.someObject doSomethingThatTakesSomeTimesWithCompletionBlock:^(NSString *result) {
        [expectation fulfill];
    }];
    [self waitForExpectationsWithTimeout:5.0 handler:^(NSError *error) {
    }];
}];
}

• These performance measure block gets executed for 10 times consecutively & then the average is calculated, & on the basis of this average performance result gets created & baseline is accepted for further evaluation.
• The performance result is compared with the previous test results & baseline with a customizable max standard deviation.

Run all tests by choosing Product > Test. Click the Test Navigator icon to view the status and results of the tests. You can add a test target to a project (or add a class to a test) by clicking the Add (plus) button in the bottom-left corner of the test navigator. To view the source code for a particular test, select it from the test list. The file opens in the source code editor.