Proper syntax for calling a particular UDF - excel

Question

This has reference to SO question Find all other cells with same adjacent element and data reproduced below to avoid cross reference.
I have an excel spreadsheet with the following columns
• A: City
• B: State
• C: Other cities that are in the same state as column A
For example, the result may look like this:
City
State
Other cities in State
Philadelphia
Pennsylvania
Pitsburgh
Pitsburgh
Pennsylvania
Philadelphia
San Diego
California
Palo Alto, Mountain View, LA, San Jose, Houston
Palo Alto
California
San Jose, Mountain View, San Diego
Mountain View
California
San Jose, LA, Palo Alto, San Diego
LA
California
San Jose, Mountain View, Palo Alto, San Diego
San Jose
California
LA, Mountain View, Palo Alto, San Diego
Austin
Texas
Houston, Dallas
Houston
Texas
Austin, Dallas
Dallas
Texas
Dallas, Houston
It was answered by user4039065 who advised to use an UDF and the code is as follows.
Option Explicit
Function CITYJOIN(rst As Range, sst As String, rct As Range, _
Optional sct As String = "", _
Optional bIncludeSelf As Boolean = False, _
Optional delim As String = ", ")
Dim r As Long
Static dict As Object
If dict Is Nothing Then
Set dict = CreateObject("Scripting.Dictionary")
dict.compareMode = vbTextCompare
End If
dict.RemoveAll
'truncate any full column references to the .UsedRange
Set rst = Intersect(rst, rst.Parent.UsedRange)
'set the cities to the same size as the states
Set rct = rct.Resize(rst.Rows.Count, rst.Columns.Count)
'loop through the cells to create unique dictionary keys
For r = 1 To rst.Cells.Count
If LCase(rst(r).Value2) = LCase(sst) Then
dict.Item(StrConv(rct(r).Value2, vbProperCase)) = vbNullString
End If
Next r
'get rid of 'self-city'
If Not bIncludeSelf Then
dict.Remove sct
End If
'return a delimited string
CITYJOIN = Join(dict.keys, delim)
End Function
It gives correct answer when used in worksheet as per following formula.
=CITYJOIN(B:B,B2,A:A,A2)
My level in VBA is elementary and I want to understand the Function code fully by stepping through the code using F8 key. With this in view I coded the following Test sub.
Sub test()
Call CITYJOIN("B: B", B2, "A: A", A2)
'CITYJOIN B: B , B2, A: A , A2
End Sub
I am getting an error at the following line in Function code stating compiler error.
CITYJOIN = Join(dict.keys, delim)
Can someone help me and provide proper code of test sub explaining the mistake in the above code of test sub.
Thanks

Answer 1

Please, call the function in this way:
Sub test()
Debug.print CITYJOIN(Range("B:B"), Range("B2").value, Range("A:A"), Range("A2").value)
End Sub
And see the result in Immediate Window (Ctrl + G being in VBE (Visual Basic for Applications Editor).