Handling Errors in Script Extensions

During execution of the script extension’s services, different errors may occur. For example, the user may specify an incorrect value for a runtime object’s property or a keyword test operation’s parameter, an action may fail to create the checkpoint due to a certain reason, and so on. Script extensions must properly handle such situations.

To handle exceptions that may occur in script extensions, you can use “native” means of the scripting languages that are used to develop extensions -- VBScript and JScript.

In VBScript, you can handle errors using the On Error Resume Next statement in conjunction with the Err object. The On Error Resume Next statement turns error handling on and commands the VBScript engine to continue script execution even if an error occurs. After executing problematic statements, you can check the Err object to see if any of them raised an error:

In JScript, you can handle exceptions using the try...catch...finally statement. The try block contains code that may raise an error, the catch block -- code that handles the error, the finally block -- code that is executed regardless of whether or not an exception occurs in the try block:

For more information about exception handling in VBScript and JScript, refer to the MSDN Library. For example, you can see the description of the On Error statement and Err object to learn more about exception handling in VBScript, and the description of the try...catch...finally statement and Error object to learn more about exception handling in JScript.

Besides handling exceptional situations, script extensions should include means to notify a user about occurred errors. The way in which the script extension’s services can do this depends on the service type -- action, object, or keyword test operation.

Record-time and design-time actions can notify a user about errors using the aqDlg.ShowError or aqDlg.MessageDlg methods. For example:

As for runtime objects, since they are supposed to be used during execution of automated tests, error notifications must be done programmatically, not visually. To illustrate possible solutions, suppose that the script extension provides the SampleObject runtime object and this object has the Number property that can hold integer values:

In the set method of the Number property, we would like to report an error if the specified value cannot be converted into an integer. We can do this in one of the following ways:

• Use the Log.Error or Log.Warning method to post an error or warning message to the test log. For example:

  JScript

  VBScript

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  JScript

  function SetNumber(Value)
  {
    try
    {
      number = aqConvert.VarToInt(Value);
    }
    catch (e)
    {
      Log.Error("Unable to set the Number property value.", e.description);
    }
  }

  VBScript

  Sub SetNumber(Value)
    On Error Resume Next
  
    number = aqConvert.VarToInt(Value)
  
    If Err.Number <> 0 Then
      Log.Error "Unable to set the Number property value.", Err.Description
    End If
  End Sub

• Add a special property or method that will return the status of the last method execution. The object’s members should set the status value before returning the control flow to the caller routine. The value 0 can correspond to successful execution, any other value - to error.

  The example below illustrates this approach. It extends our sample object with the LastStatus property that returns the status code of the last operation performed over the object:

  JScript

  VBScript

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  JScript

  var number;
  var last_status;  // An internal variable that holds the LastStatus property value
  
  // The set method of the Number property
  function SetNumber(Value)
  {
    try
    {
      number = aqConvert.VarToInt(Value);
      last_status = 0;  // The property value has been successfully modified
    }
    catch (e)
    {
      last_status = e.number;  // An error indicating that Value could not be converted to an integer
    }
  }
  
  // The Get method of the LastStatus property
  function GetLastStatus()
  {
    return last_status;
  }

  VBScript

  Dim last_status  ' An internal variable that holds the LastStatus property value
  
  Sub SetNumber(Value)
    On Error Resume Next
  
    number = aqConvert.VarToInt(Value)
    last_status = Err.Number
    ' last_status is 0 if Value was successfully converted to an integer.
    ' Otherwise, last_status contains the error code.
  End Sub
  
  ' The get method of the LastStatus property
  Function GetLastStatus
    GetLastStatus = last_status
  End Function

  Here is how you can check the object’s LastStatus property from test scripts:

  JavaScript, JScript

  Python

  VBScript

  DelphiScript

  C++Script, C#Script

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  JavaScript, JScript

  function UsingLastStatus()
  {
    // This line causes an internal error in SampleObject
    SampleObject.Number = "not a number";
  
    if (SampleObject.LastStatus != 0)
      Log.Error("Unable to set the Number property value");
  }

  Python

  def UsingLastStatus():
    # This line causes an internal error in SampleObject
    SampleObject.Number = "not a number"
  
    if (SampleObject.LastStatus != 0):
      Log.Error("Unable to set the Number property value")

  VBScript

  Sub UsingLastStatus
    ' This line causes an internal error in SampleObject
    SampleObject.Number = "not a number"
  
    If SampleObject.LastStatus <> 0 Then
      Log.Error "Unable to set the Number property value"
    End If
  End Sub

  DelphiScript

  procedure UsingLastStatus;
  begin
    // This line causes an internal error in SampleObject
    SampleObject.Number := 'not a number';
  
    if SampleObject.LastStatus <> 0 then
      Log.Error('Unable to set the Number property value');
  end;

  C++Script, C#Script

  function UsingLastStatus()
  {
    // This line causes an internal error in SampleObject
    SampleObject["Number"] = "not a number";
  
    if (SampleObject["LastStatus"] != 0)
      Log["Error"]("Unable to set the Number property value");
  }

• Return the status of the object’s method execution via the method’s return value. This approach can only be used by the object’s methods that are not supposed to return other values. It cannot be used in the get and set methods of properties.

  To illustrate this approach, suppose that our sample object has the IncNumber method that increases the stored number by the specified value. To prevent exceptional situations, this method verifies the type of the passed parameter and returns an error code if the parameter type is invalid (that is, any but integer):

  JScript

  VBScript

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  JScript

  var number;
  
  function IncNumber(Value)
  {
    var result = 0;
  
    if (aqObject.GetVarType(Value) == varInteger)
      number += Value
    else
      result = 1;
  
    return result;
  }

  VBScript

  Dim number
  
  Function IncNumber(Value)
    Dim result
    result = 0
  
    If (aqObject.GetVarType(Value) = varInteger) Or (aqObject.GetVarType(Value) = varSmallInt) Then
      number = number + Value
    Else
      result = 1
    End If
  
    IncNumber = result
  End Function

  The example below demonstrates how you can check the method’s return status in the test code:

  JavaScript, JScript

  Python

  VBScript

  DelphiScript

  C++Script, C#Script

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  JavaScript, JScript

  function UsingReturn()
  {
    SampleObject.Number = 42;
  
    var res = SampleObject.IncNumber(5);   // OK, ...
    if (res != 0)
      Log.Error("Unable to increment the Number property");    // so this line will not be executed
  
    res = SampleObject.IncNumber(true);    // The parameter type is incorrect, ...
    if (res != 0)
      Log.Error("Unable to increment the Number property");    // ... so we'll have this error posted to the log
  }

  Python

  def UsingReturn():
    SampleObject.Number = 42
  
    res = SampleObject.IncNumber(5)   # OK, ...
    if (res != 0):
      Log.Error("Unable to increment the Number property")    # so this line will not be executed
  
    res = SampleObject.IncNumber(True)    # The parameter type is incorrect, ...
    if (res != 0):
      Log.Error("Unable to increment the Number property")    # ... so we'll have this error posted to the log

  VBScript

  Sub UsingReturn
    Dim res
  
    SampleObject.Number = 42
  
    res = SampleObject.IncNumber(5)     ' OK, ...
    If res <> 0 Then
      Log.Error "Unable to increment the Number property"    ' ... so this line will not be executed
    End If
  
    res = SampleObject.IncNumber(True)  ' The parameter type is incorrect, ...
    If res <> 0 Then
      Log.Error "Unable to increment the Number property"    ' ... so we'll have this error posted to the log
    End If
  End Sub

  DelphiScript

  procedure UsingReturn;
  var res;
  begin
    SampleObject.Number := 42;
  
    res := SampleObject.IncNumber(5);      // OK, ...
    if res <> 0 then
      Log.Error('Unable to increment the Number property');    // so this line will not be executed
  
    res := SampleObject.IncNumber(true);    // The parameter type is incorrect, ...
    if res <> 0 then
      Log.Error('Unable to increment the Number property');    // ... so we'll have this error posted to the log
  end;

  C++Script, C#Script

  function UsingReturn()
  {
    SampleObject["Number"] = 42;
  
    var res = SampleObject["IncNumber"](5);    // OK, ...
    if (res != 0)
      Log["Error"]("Unable to increment the Number property");    // so this line will not be executed
  
    res = SampleObject["IncNumber"](true);     // The parameter type is incorrect, ...
    if (res != 0)
      Log["Error"]("Unable to increment the Number property");    // ... so we'll have this error posted to the log
  }

Keyword test operations can use a combination of the described approaches. For instance, at design-time they can display errors using the aqDlg.ShowError or aqDlg.MessageDlg methods, at run time -- post error messages to the test log using the Log.Error or Log.Warning method.