public async Task CheckRefreshTokenNull_Test() { _refreshTokenRepositoryMock.Setup(repo => repo.GetAsync(It.IsAny <System.Linq.Expressions.Expression <Func <RefreshTokens, bool> > >())).Returns(async() => { return(null); }); var ex = await Assert.ThrowsExceptionAsync <HttpStatusCodeException>(() => _refreshTokenService.CheckRefreshTokenAsync(RefreshToken)); Assert.AreEqual("Such refreshToken doesn't exist", ex.Message); Assert.AreEqual(HttpStatusCode.NotFound, ex.StatusCode); }