Remove equal periods duration after inserting period into TimePeriodC…

…hain

Sources/SwiftDate/TimePeriod/Groups/TimePeriodChain.swift

@@ -94,9 +94,9 @@ open class TimePeriodChain: TimePeriodGroup {
 		//Shift all periods after inserted period
 		for i in 0..<periods.count {
 			if i > index && i > 0 {
-				let currentPeriod = TimePeriod(start: period.start, end: period.end)
+				let duration = periods[i].duration
 				periods[i].start = periods[i - 1].end
-				periods[i].end = periods[i].start!.addingTimeInterval(currentPeriod.duration)
+				periods[i].end = periods[i].start!.addingTimeInterval(duration)
 			}
 		}
 

Tests/SwiftDateTests/TestTimePeriodChain.swift

@@ -8,7 +8,7 @@
 //  Copyright © 2019 Daniele Margutti. Licensed under MIT License.
 //
 
-import SwiftDate
+@testable import SwiftDate
 import XCTest
 
 class TestTimePeriodChain: XCTestCase {
@@ -25,5 +25,22 @@ class TestTimePeriodChain: XCTestCase {
 		XCTAssert(chain.start == periods.first!.start, "TimePeriodChain initial start not equals to source period start")
 		XCTAssert(chain.end == periods.last!.end, "TimePeriodChain initial end not equals to source period end")
 	}
-
+
+	func testInsert () {
+		let chain = TimePeriodChain(periods)
+		let period = TimePeriod(start: .init(year: 2020, month: 1, day: 1), end: .init(year: 2020, month: 1, day: 20))
+
+		let originalDuration_0 = chain.periods[0].duration
+		let originalDuration_1 = chain.periods[1].duration
+		let originalDuration_2 = chain.periods[2].duration
+		let originalDuration_3 = chain.periods[3].duration
+
+		chain.insert(period, at: 2)
+
+		XCTAssert(chain.periods[0].duration == originalDuration_0, "Unexpected duration of 0 period– Actual: \(chain.periods[0].duration) – Expected: \(originalDuration_0)")
+		XCTAssert(chain.periods[1].duration == originalDuration_1, "Unexpected duration of 1 period – Actual: \(chain.periods[1].duration) – Expected: \(originalDuration_1)")
+		XCTAssert(chain.periods[2].duration == period.duration, "Unexpected duration of 2 period – Actual: \(chain.periods[2].duration) – Expected: \(period.duration)")
+		XCTAssert(chain.periods[3].duration == originalDuration_2, "Unexpected duration of 3 period – Actual: \(chain.periods[3].duration) – Expected: \(originalDuration_2)")
+		XCTAssert(chain.periods[4].duration == originalDuration_3, "Unexpected duration of 4 period – Actual: \(chain.periods[4].duration) – Expected: \(originalDuration_3)")
+	}
 }