Changed request to hold mutable copy and added unit tests to test the same

Author: Vikas Dadheech

MSGraphCoreSDK/MSGraphCoreSDK/Common/Session Tasks/MSURLSessionTask.m

@@ -24,7 +24,7 @@ - (instancetype)initWithRequest:(NSMutableURLRequest *)request
     if (self)
     {
         _client = client;
-        _request = request;
+        _request = [request mutableCopy];
     }
     return self;
 }

MSGraphCoreSDK/MSGraphCoreSDKTests/SessionTask/MSURLSessionTaskTests.m

@@ -40,9 +40,17 @@ - (void)testInitFailsWithNilRequest{
     XCTAssertThrows([[MSURLSessionTask alloc] initWithRequest:nil client:self.mockClient]);
 }
 
-- (void)testInitMSURLSessionTaskState{
+- (void)testInitWithNonMutableRequest {
+    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:self.testBaseURL];
+    MSURLSessionTask *sessionTask = [[MSURLSessionTask alloc] initWithRequest:urlRequest client:self.mockClient];
+    XCTAssertTrue([sessionTask.request isKindOfClass:[NSMutableURLRequest class]]);
+    XCTAssertNotEqual(urlRequest, sessionTask.request);
+}
+
+- (void)testInitMSURLSessionTask{
     MSURLSessionTask *msURLSessionTask= [[MSURLSessionTask alloc] initWithRequest:self.requestForMock client:self.mockClient];
     XCTAssertEqual(msURLSessionTask.client, self.mockClient);
+    XCTAssertNotEqual(msURLSessionTask.request, self.requestForMock);
 }
 
 - (void)testSetInnerTask{