C#, EF 6 - DBContext not opening connection

Question

I'm working with Oracle.ManagedDataAccess (v. 4.122.19.1) and Entity Framework (v. 6.0.0.0).

I created a simple context like this:

public class FooContext : DbContext
{
    public FooContext() : base(new OracleConnection(Connection.connection),true)
    {
        Database.SetInitializer<FooContext>(null);
        Configuration.LazyLoadingEnabled = false;
    }
}

and test method:

[TestMethod]
private static void TestIsConnectionOpen() 
{
    using (var db = new FooContext())
    {
        Assert.AreEqual(ConnectionState.Open, db.Database.Connection.State);
    }
}

I expected, that in this case, connection will be automatically open, like in this e.g. https://github.com/entityframeworktutorial/EF6-DBFirst-Demo , but the test fails.

Could someone explain to me why?

Connection.connection is a valid connection string, because when I change test method to:

[TestMethod]
private static void TestIsConnectionOpen() 
{
    using (var db = new FooContext())
    {
        db.Database.Connection.Open();
        Assert.AreEqual(ConnectionState.Open, db.Database.Connection.State);
    }
}

then the test passed.