TestingSchemaLock tests if a feature class or table has a schema lock. Any tool that alters schema will require a schema lock to be placed on the input data. If a tool requires a schema lock and is unable to acquire one an error message is provided.
import arcpy
data = arcpy.GetParameterAsText(0)
isLocked = arcpy.TextSchemaLock(data)
if lockTest:
arcpy.AddField_management(data,"Flag","long")
else:
print "Unable to acquire the necessary schema lock to add the new field"