FindTest.cs

[Fact]
public void Find_TestClassObjectPassed_ProperMethodCalled()
{
    var testObject = new TestClass(){Id = 1};
    var testList = new List<TestClass>() {testObject};

    var dbSetMock = new Mock<DbSet<TestClass>>();
    dbSetMock.As<IQueryable<TestClass>>().Setup(x => x.Provider).Returns(testList.AsQueryable().Provider);
    dbSetMock.As<IQueryable<TestClass>>().Setup(x => x.Expression).Returns(testList.AsQueryable().Expression);
    dbSetMock.As<IQueryable<TestClass>>().Setup(x => x.ElementType).Returns(testList.AsQueryable().ElementType);
    dbSetMock.As<IQueryable<TestClass>>().Setup(x => x.GetEnumerator()).Returns(testList.AsQueryable().GetEnumerator());

    var context = new Mock<DbContext>();
    context.Setup(x => x.Set<TestClass>()).Returns(dbSetMock.Object);

    var repository = new Repository<TestClass>(context.Object);

    var result = repository.Find(x => x.Id == 1);

    Assert.Equal(testList, result.ToList());
}