How to mock a Generics<T> class that actually used to fetch data from database

Question

I have a Base class where i can find different generic methods like

public class EntityRepositoryBase<T> : IDisposable, IEntityRepository<T> where T : class
{
//Context is application DbContext class
public Context DataContext
{
    get { return Context.GetContext(); }
}


public virtual IQueryable<T> GetAll()
{
    return DataContext.Set<T>().AsQueryable();
}

 public virtual bool Any(Expression<Func<T, bool>> predicate)
 {
     return DataContext.Set<T>().Any(predicate);
 }

I want to mock this DataContext(which has connection with real database) by in-memory Database Context so i can write different tests for the following method.

public List<DtoTypeEntity> GetPlantData()
{
    List<DtoTypeEntity> lstEntity = new List<DtoTypeEntity>();
    using (var PlantTypeRepo = new EntityRepositoryBase<PlantType>())
    {
        // Some Logic here...
        lstEntity = PlantTypeRepo.ToList();
    }
    return lstEntity;
}

I have added my custom DbContext class just to unit tests

 public class MyTestDbContext : DbContext
 {
     public MyTestDbContext(DbContextOptions<MyTestDbContext> options) : base(options)
     {
     }

     public DbSet<PlantType> PlantTypes { get; set; }
 }

In test class something like this

public class MasterDataManagerTests
{
    private readonly DbContextOptions<MyTestDbContext> _options;


    public MasterDataManagerTests()
    {
        
        // Set up in-memory database options
        _options = new DbContextOptionsBuilder<MyTestDbContext>()
            .UseInMemoryDatabase(databaseName: "MyTestDb")
            .Options;
    }

    [Theory]
    [InlineData("PLANT_TYPE1")]
    public void MasterDataManager_GetAllMasterData_ReturnPlantList(string screenCode)
    {
        // Arrange
        var context = new MyTestDbContext(_options);
        context.PlantTypes.Add(new PlantType { PlantType_ID = 123, Code = "Code1", Name = "ABC", ValidStartDate = DateTime.Now, ValidEndtDate = DateTime.Now});
        context.PlantTypes.Add(new PlantType { PlantType_ID = 456, Code = "Code2", Name = "XYZ", ValidStartDate = DateTime.Now, ValidEndtDate = DateTime.Now});
        context.SaveChanges();

        var dbRepo = new EntityRepositoryBase<PlantType>() {};
        dbRepo.DataContext = new GaiaTestDbContext(_options);

        // Act
        
    }

But i am unable to mock real dbcontext with in-memory dbcontext.It shows me unable to assign a value to dbRepo.DataContext