Goal:
Create a unit test for a EF repository query. As we all know unit tests are infrastructure agnostic and therefore have no kowledge of for example external services, databases, etc. So how can we create a unit test for a repository query without hitting the DB? Mocked DbSet to the rescue:
Solution:
Create an extension method on collections that can be used to mock the data/collections returned by EF instead of hitting the DB.
//A List of allocations for a gas system that we want to return when the EF LINQ query is executed
var allocationVOMockDbSet = new List
{
new AllocationVO
{
LocationId = -1,
ContractId = -1,
NominationId = null,
AllocatedQuantity = 1000,
AdjustmentIndicatorType = AdjustmentIndicatorType.Measurement,
GasDayId = -100,
GasDay = new GasDay(null, DateTime.Today),
AccountingPeriod = new YearMonth(2016, 10)
},
//new
new AllocationVO
{
LocationId = -1,
ContractId = -1,
NominationId = null,
AllocatedQuantity = 1500,
AdjustmentIndicatorType = AdjustmentIndicatorType.Other,
GasDayId = -100,
GasDay = new GasDay(null, DateTime.Today),
AccountingPeriod = new YearMonth(2016, 10)
},
}
.AsMockDbSet(); //here we define the list as a mocked set
//Now we use the StructureMap container to create an inject the DbContext of IAfterFlowContext
var afterFlowContextMock = thisContainer.InstantiateAndInjectMock();
//Now we add the setup for the mocked context on Set of AllocationVO (a domain entity) that returns the mocked set
afterFlowContextMock.Setup(s => s.Set()).Returns(allocationVOMockDbSet.Object);
//Here is the extension for collections on DbSet that makes it possible to mock all the different implementations of the DbSet
public static Mock<DbSet> AsMockDbSet(this ICollection source) where T : class
{
var queryable = source.AsQueryable();
var dbSet = new Mock<DbSet>();
dbSet.As<IQueryable>().Setup(m => m.Provider).Returns(queryable.Provider);
dbSet.As<IQueryable>().Setup(m => m.Expression).Returns(queryable.Expression);
dbSet.As<IQueryable>().Setup(m => m.ElementType).Returns(queryable.ElementType);
dbSet.As<IQueryable>().Setup(m => m.GetEnumerator()).Returns(queryable.GetEnumerator);
dbSet.Setup(s => s.Add(It.IsAny())).Callback(source.Add);
dbSet.Setup(s => s.Include(It.IsAny())).Returns(dbSet.Object);
dbSet.Setup(x => x.AsNoTracking()).Returns(dbSet.Object);
return dbSet;
}