NullReferenceException vb.net單元測試錯誤

Question

做單元測試的一些作業，並在所有老實說，我只是不明白爲什麼我得到這個錯誤。

我有一個簡單的方法，選擇所有文本時選項卡和測試，如果實際textbox1被選中。我只是不明白爲什麼我在target.txtbox1_Enter（發送者，e）得到nullReferenceException

我越來越生氣，因爲這看起來很容易。

任何幫助，我將不勝感激。

Private Sub txtbox1_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtbox1.enter 
    Dim txtBox As TextBox 
    txtBox = CType(sender, TextBox) 
    txtBox.SelectAll() 
End Sub 

    <TestMethod(), DeploymentItem("frmtesting.exe")> 
Public Sub txtCustomer_EnterTest() 
    Dim target As frmtesting_Accessor = New frmtesting_Accessor ' TODO: Initialize to an appropriate value 
    Dim sender As Object = Nothing ' TODO: Initialize to an appropriate value 
    Dim e As EventArgs = Nothing ' TODO: Initialize to an appropriate value 

    Dim expected As String 
    Dim actual As String 
    target.txtbox1.Text = "bob" 
    target.txtbox1.SelectAll() 
    expected = "bob" 

    target.txtbox1_Enter(sender, e) 

    actual = target.txtbox1.SelectedText 
    Assert.AreEqual(expected, actual, "not equal") 
End Sub 

Answer 1

這將是正確的做法。

'''<summary> 
    '''A test for TextBox1_Enter 
    '''</summary> 
    <TestMethod(), _ 
    DeploymentItem("frmtesting.exe")> _ 
    Public Sub TextBox1_EnterTest() 
     Dim target As frmtesting.exe_Accessor = New frmtesting.exe_Accessor() 
     Dim sender As Object = target.TextBox1 
     Dim e As EventArgs = Nothing 

     target.txtBox1.Text = "bob" 

     target.txtBox1_Enter(sender, e) 

     Assert.AreEqual("bob", target.txtBox1.SelectedText, "not equal") 

    End Sub