mkdir swifttesting
cd swifttesting swift build --init library
(replace library with your executable of app)

create following hierarchy
package
---sources
---testing
---app_files

public struct swift_example
{
    let title: String
    let completed: Bool
    let order: Int
    
    init(title: String, completed: Bool, order: Int)
    {
        self.title = title
        self.completed = completed
        self.order = order
    }
}

here we have initialized title,completed,order variables
Let's build that in Swift and we'll put it in Sources/swift_example.swift

Setup unit test class separate, so in package/testing create unit test class.
we can call this class as swift_unittesting.swift
and we'll write a simple unit test to get us started:

class TestURL : XCTestCase {
    static var allTests = {
        return [
            ("test_URLStrings", test_URLStrings),
            ("test_fileURLWithPath_relativeToURL", test_fileURLWithPath_relativeToURL),
            ("test_fileURLWithPath", test_fileURLWithPath),
            ("test_fileURLWithPath_isDirectory", test_fileURLWithPath_isDirectory),
            // Other tests go here
        ]
    }()

    func test_fileURLWithPath_relativeToURL() {
        // Write your test here. Most of the XCTAssert macros you are familiar with are available.
        XCTAssertTrue(theBestNumber == 42, "The number is wrong")
    }

    // Other tests go here

To test under Linux, we need to do two things.
Firstly we need to provide a list all the unit test methods in the test class as a static variable and secondly we need to list our test classes in a file called LinuxMain.swift.

we need to add the following block of code in linux for making tests run

#if os(Linux)
extension FooTests {
	static var allTests : [(String, TestURL -> () throws -> Void)] {
		return [
      XCTMain([testCase(TestNSString.allTests), testCase(TestNSArray.allTests), testCase(TestNSDictionary.allTests)])
		]
	}
}
#endif 

//later this is from orginal document.

We are currently investigating ideas on how to make these additional steps for test discovery automatic
when running on the Swift runtime.

The XCTMain function does not return, and will cause your test app to exit with either 0
for success or 1 for failure. Certain command line arguments can be used to modify the test runner behavior:

• A particular test or test case can be selected to execute. For example:

$ ./FooTests Tests.FooTestCase/testFoo  # Run a single test case
$ ./FooTests Tests.FooTestCase          # Run all the tests in FooTestCase

• Tests can be listed, instead of executed.

$ ./FooTests --list-tests
Listing 4 tests in FooTests.xctest:

Tests.FooTestCase/testFoo
Tests.FooTestCase/testBar
Tests.BarTestCase/test123

$ ./FooTests --dump-tests-json
{"tests":[{"tests":[{"tests":[{"name":"testFoo"},{"name":"testBar"}],
"name":"Tests.FooTestCase"},{"tests":[{"name":"test123"}],"name":"Tests.BarTestCase"}],"name":"Tests.xctest"}],"name":"All tests"}