IsAccountNumberVerified returns a boolean value, true or false.
A long is a 64-bit integer, not really appropriate for the return value.
Your unit test code should be:
public void ID_1_TestMethodIsAccountNumberVerified_BVAValidNumberMin()
long accountNumber = 32186587;
bool expected = true;
BankAccount bankAccount = new BankAccount(20.00, "Mr. Bryan Walton");
bool verified = bankAccount.IsAccountNumberVerified(accountNumber);
You really can't use the account number in your unit test because it's randomly generated. Also, the random number generator is seeded with the current time when the Random object is created, so you can't even reliably get the same account number back from it.
But, this test is going to fail at a very high rate. You're testing against a very specific account number in the a range of 900,000,000 account numbers.
You wouldn't have a method called "IsAccountNumberVerified" that takes an account number as a value. The account number would be maintained and verified internally by the BackAccount class, only exposing the account number as a readonly property.