public void GetPlainTextTestEmail_WhenInvoke_ShouldReturnNotNullEmailMessage() { _webHostEnvMock.DefaultValue = DefaultValue.Mock; var provider = _webHostEnvMock.Object.ContentRootFileProvider; var providerMock = Mock.Get(provider); var fileMock = new PhysicalFileInfo (new FileInfo(_fileInfoPath)); providerMock.Setup(x => x.GetFileInfo(It.IsAny <string>())) .Returns(fileMock); EmailTemplates.Initialize(_webHostEnvMock.Object); DateTime testDate = new DateTime(2020, 1, 1); string emailMessage = EmailTemplates.GetPlainTextTestEmail(testDate); Assert.IsNotNull(emailMessage); }