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TDD -- From SME Spreadsheet to TestCase to Code

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In " Unit Test Case, Subject Matter Experts and Requirements" I suggested that it's often pretty easy to get a spreadsheet of full-worked out examples from subject-matter experts. Indeed, if your following TDD, that spreadsheet of examples is solid gold.

Let's consider something relatively simple. Let's say we're working on some fancy calculations. Our users explain until they're blue in the face. We take careful notes. We think we understand. To confirm, we ask for a simple spreadsheet with inputs and outputs.

We get something like the following. The latitudes and longitudes are inputs. The ranges and bearings are outputs. [The math can be seen at " Calculate distance, bearing and more between Latitude/Longitude points".]

Latitude 1 Longitude 1 Latitude 2 Longitude 2 range bearing
50 21 50N 004 09 25W 42 21 04N 071 02 27W 2805 nm 260 07 38

Only it has a a few more rows with different examples. Equator Crossing. Prime Meridian Crossing. All the usual suspects.

TDD Means Making Test Cases

Step one, then, is to parse the spreadsheet full of examples and create some domain-specific examples. Since it's far, far easier to work with .CSV files, we'll presume that we can save the carefully-crafted spreadsheet as a simple .CSV with the columns shown above.

Step two will be to create working Python code from the domain-specific examples.

The creation of test cases is a matter of building some intermediate representation out of the spreadsheet. This is where plenty of parsing and obscure special-case data handling may be necessary.

`from __future__ import divisionimport csvfrom collections import namedtupleimport relatlon_pat= re.compile("(\d+)\s+(\d+)\s+(\d+)([NSWE])")def latlon( txt ):  match= latlon_pat.match( txt )  d, m, s, h = match.groups()  return float(d)+float(m)/60+float(s)/3600, hangle_pat= re.compile("(\d+)\s+(\d+)\s+(\d+)")def angle( txt ):  match= angle_pat.match( txt )  d, m, s = match.groups()  return float(d)+float(m)/60+float(s)/3600range_pat= re.compile("(\d+)\s*(\D+)")def range( txt ):  match= range_pat.match( txt )  d, units = match.groups()  return float(d), unitsRangeBearing= namedtuple("RangeBearing","lat1,lon1,lat2,lon2,rng,brg")def test_iter( filename="sample_data.csv" ):  with open(filename,"r") as source:      rdr= csv.DictReader( source )      for row in rdr:          print row          tc= RangeBearing(              latlon(row['Latitude 1']),  latlon(row['Longitude 1']),              latlon(row['Latitude 2']),  latlon(row['Longitude 2']),              range(row['range']),              angle(row['bearing'])              )          yield tc    for tc in test_iter():  print tc`
This shows a simple template with values filled in. Often, we have to generate a hair more than this. A few imports, a "unittest.main()" is usually sufficient to transform a spreadsheet into unit tests that we can confidently use for test-driven development.

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