public async void ChangeAuthenticationHeader_ShouldChangeAuthenticationHeader() { // Arrange const string testHeader = "TestHeader"; _mockHttpMessageHandler .Protected() .Setup <Task <HttpResponseMessage> >( "SendAsync", ItExpr.IsAny <HttpRequestMessage>(), ItExpr.IsAny <CancellationToken>() ) .ReturnsAsync(new HttpResponseMessage { StatusCode = HttpStatusCode.OK }) .Verifiable(); // Act _gateway.ChangeAuthenticationHeader(testHeader); await _gateway.GetAsync(It.IsAny <string>()); // Assert _mockHttpMessageHandler .Protected() .Verify( "SendAsync", Times.Once(), ItExpr.Is <HttpRequestMessage>(req => req.Headers.Authorization.ToString() == testHeader), ItExpr.IsAny <CancellationToken>() ); }