How to do unit tests for file reading functionality? C#

So far I've been using the AAA method, which I would like to deploy into a set of 'mock-up' tests to test to see if a file exists, and if a file can be read etc..

The type of code I've been using is as followed..

[TestMethod]
public void Mul_TestValues0and0_EvaluatesTo0() {
    // Arrange
    var testArgument1 = 0;
    var testArgument2 = 0;
    var expectedResult = 0;

    // Act
    var actualResult = testedClass.Mul(testArgument1, testArgument2);

    //Assert
    var failMessage = String.Format(@"{0} * {1} evaluates to {2}, actual test result was {3}", testArgument1, testArgument2, expectedResult, actualResult);
    Assert.AreEqual(expectedResult, actualResult, failMessage);
}

Hope someone can help thanks!