Test en debut de macro si =""

Sub test()
Dim Mes_Cellules As Range, Une_Cellule As Range, t$
Set Mes_Cellules = Range("L10:L100")
For Each Une_Cellule In Mes_Cellules
If IsEmpty(Une_Cellule) Or Not IsDate(Une_Cellule) Then
t = t & Une_Cellule.Address(0, 0) & vbLf
End If
Next
MsgBox "Renseigner une date dans les cellules suivante(s)." & vbLf & t
End Sub

If Application.WorksheetFunction.Sum(Range("L10:L100")) = 0 Then
  ....
Else
  ....
End If

Sub test_2()
Dim Mes_Cellules As Range, Une_Cellule As Range, t$
Set Mes_Cellules = Range("A1:A5")
For Each Une_Cellule In Mes_Cellules
If IsEmpty(Une_Cellule) Or Not IsDate(Une_Cellule) Then
t = t & Une_Cellule.Address(0, 0) & vbLf
End If
Next
If Len(t) > 0 Then
MsgBox "Renseigner les cellules suivantes : " & vbLf & t
Else
'
End If
End Sub

Sub MACRO_HONORIS_PIERREJEANUS_EXCELLUS_VBASTUS_MASTERUS()
With ActiveSheet
MsgBox IIf(Application.WorksheetFunction.Sum(.Range("A1:A5")) = 0, "Renseigner", "Saisie OK")
End With
End Sub