Fit Spreadsheet

Starting Fit

To use fit, you create a web page that has tables in it; the tables specify tests. (There are other options but that is easiest.) In this case, I’m using Microsoft Word(tm) and saving the file in HTML format.

The fit FileRunner acts as a filter: given a web page, it copies text outside of tables as is, and runs your program on the table entries. Some table entries represent tests that can pass or fail; fit colors them green or red respectively. The output is another HTML file.

Fit will also put a summary in the file if you put in a table like this:

With this tool, you don’t manipulate screen elements directly. Instead, you work with an abstraction of them. To me, it feels like talking to somebody over the phone, trying to tell them how to use an application. (“In cell cee seventeen, put equals a one; then go to a one and type ‘fish’.”)

This article shows the input to fit; the result of running it is here.

Programming and Configuration Notes

Fit is a tool for customers and testers, but programmers will use it as well, and will have to write some of the fixtures the team uses. In this paper, I’ve tried to use the framework mostly straight out of the box.

The CLASSPATH needs to include fit.jar (both in the DOS window and the IDE). The runner command I’m using is:

java fit.FileRunner FirstFit-in.htm FirstFit-out.htm

When I do this on the file I have so far, it creates the output file and writes this to the console:

0 right, 0 wrong, 0 ignored, 0 exceptions

Fixtures

Tables in the input file have the name of a fixture in the first row. A fixture is a class that knows how to process the table. Fit comes with several fixtures built in, and programmers can create others.

One simple fixture is the ColumnFixture. In this fixture, the first row is the fixture name, and the second row has the names of data. If a name ends without parentheses, it is regarded as a field to fill in; with parentheses, it’s treated as a method (function) call. The fixture fills in all the data fields, and then calls the methods to verify that they return the expected results.

Another standard fixture is the ActionFixture. This one consists of a series of commands. These include:

• start classname: Creates an object of the specified class
• enter field value: Sets the field to the value
• press button-name: Calls the method corresponding to the button
• check method value: Checks that the method returns the expected value

The ActionFixture ignores anything past the first three columns; we’ll use the fourth column for comments.

So, we’re finally ready to start our application.

fit.ActionFixture
start	Spreadsheet	Create a new spreadsheet.

This test doesn’t ask for much, but of course it fails. (There isn’t any code yet!)

0 right, 0 wrong, 0 ignored, 1 exceptions

Programmer Notes

The exception is thrown because the Spreadsheet object doesn’t exist. To create it as simply as possible, make it extend Fixture:

import fit.Fixture;

public class Spreadsheet extends Fixture {}

This gets us back to

0 right, 0 wrong, 0 ignored, 0 exceptions

I’ve put together stubs for the fixtures used in this article: Spreadsheet.java, SpreadsheetFormula.java, and Address.java; here’s a zip file containing all three.

A Few Stories

We have several things we want our spreadsheet to do:

• Track the contents of cells
• Distinguish data from formulas
• Provide both data and formula views of cells
• Support “+” for appending strings, “‘” for reversing strings, “()” for grouping, and “>” for string containment.

Cells

The spreadsheet has a number of cells, each of which has an address. Cells contain string data or formulas.

We’ll assume several screen elements:

• a1 – the cell “A1“. For “enter,” we‘ll put something in the cell; for “check,” we‘ll get its displayed value.
• b1 – the same for cell “B1”.
• formula – the formula of the last-mentioned cell.

We’ll start with a simple data cell.

fit.ActionFixture			Comments
start	Spreadsheet
enter	a1	abc
check	a1	abc	Text in cell
check	formula	abc	Formula is same. (Looks in last-mentioned cell.)

Now let’s add in a formula cell. (Note that this table omits the “start” line; this means it’s working on the same object as before. This lets us not repeat the setup, but it also makes the tests less independent.)

fit.ActionFixture			Comments
enter	a1	abc
enter	b1	=A1	Simple copying formula
check	formula	=A1	Formula is there
check	a1	abc	Original text in A1
check	b1	abc	Text was copied to B1

The essence of a spreadsheet is the automatic updates. Let’s change A1 and see it happen.

fit.ActionFixture			Comments
enter	a1	abc
enter	b1	=A1	Simple copying formula
check	b1	abc	Copied value
enter	a1	revised	Update A1
check	b1	revised	Automatically updates B1

We already have quite a few elements in use, though we haven’t specified exactly what is valid. Let’s just note the “specification debt” and move on.

• What can a cell hold? Empty string, other string, formula starts with “=”
• What’s a valid address? Letter plus digits; ignore leading 0s; case-insensitive.
• What’s a valid formula? So far, we’ve just used a simple cell reference, but we want operators too.
• What happens when a cell has an invalid formula?
• What happens when a cell refers to a cell containing a formula?
• What happens when formulas form a loop?

We’ll pursue all these, but let’s start with formulas.

Formulas

Formulas can reference formulas. We’ll use a new ColumnFixture, SpreadsheetFormula, that lets us specify the inputs and expected outputs of cells. This fixture should access the same type spreadsheet as used by Spreadsheet.

SpreadsheetFormula
a1	b1	c1	d1	a1()	b1()	c1()	d1()
data	=A1	=B1	=C1	data	data	data	data

Formulas get more interesting when there are operators available. The reverse operator (‘) is probably a good one to start with.

SpreadsheetFormula
a1	b1	b1()
abc	=A1′	cba
abc	=A1””	abc

The most useful string operator is probably append (+). Fit ignores input cells that are left blank, so we’ll explicitly use the word “blank” when we want an empty cell. The fixture will have to take this into account.

SpreadsheetFormula
a1	b1	c1	b1()	c1()
abc	=A1+A1	blank	abcabc
abc	def	=A1+B1+B1+A1	def	abcdefdefabc

We have enough features that we can demonstrate an identity: (XY)’=Y’X’. We don’t have parentheses yet, but we can simulate this by putting the parts in separate cells.

SpreadsheetFormula
a1	b1	c1	d1	e1	d1()	e1()
abc	xyz	ignored	=A1+B1	=D1′	abcxyz	zyxcba
abc	xyz	=B1′	=A1′	=C1+D1	cba	zyxcba

Parentheses can be used to group operators. Let’s re-do the previous test, allowing parentheses:

SpreadsheetFormula
a1	b1	c1	c1()
abc	xyz	=(A1+B1)’	zyxcba
abc	xyz	=B1’+A1′	zyxcba

The operator “>” tells whether one string contains another one. If the first string contains the second, the result is the second. If the first string doesn’t contain the second, the result is an empty string.

SpreadsheetFormula
a1	b1	c1	c1()
banana	ana	=A1>B1	ana
banana	bab	=A1>B1

We haven’t talked about precedence yet. The ‘ and () operators have the highest precedence, then +, then >. A1+B1+C1 is a legal expression, but A1>B1>C1 is not.

SpreadsheetFormula
a1	b1	c1	c1()
abc	xyz	=A1+B1′	abczyx
abc	xyz	=(A1+B1)’	zyxcba

SpreadsheetFormula
a1	b1	c1	d1	e1	e1()
abcdef	ghijkl	e	hgf	=A1+B1>C1+D1′	efgh

Filling in the Gaps

We have several questions left open:

• What can a cell hold? Empty string, other string, formula starts with “=”
• What’s a valid address? Letter plus digits; ignore leading 0s; case-insensitive.
• What happens when a cell has an invalid formula?
• What happens when formulas form a loop?

The previous tests made a quick pass through the system. I think of them as generative: they help define the essence of the system. But questions like the above require us to fill in the gaps. I think of tests that do things like check “corner cases,” error cases, and how features interact as elaborative; they fill in what we already have. They might find problems, but they may well work already, depending on how the system was built.

What a cell holds

We already have test cases where a cell holds a string, and where a cell holds a formula, but it would be prudent to check that the operators work correctly on empty strings. If e is the empty string and x is a non-empty string, we expect:

e‘ = e
e+e=e
e+x=x
x+e=x
e>e=e
e>x=e
x>e=e

As I go to write the test, I realize that we never specified what a cell starts with. The answer, of course, is the empty string. So we’ll rely on that: A1 will be empty.

fit.ActionFixture			Comments
start	Spreadsheet
check	a1		Verify that cell starts empty.

Then we can verify those rules about working with the empty string:

SpreadsheetFormula
a1	b1	c1	c1()	Comment
blank	blank	=A1′	blank	e’=e
blank	blank	=A1+A1	blank	e+e=e
blank	blank	=A1>A1	blank	e>e=e
blank	abc	=A1+B1	abc	e+x=x
blank	abc	=B1+A1	abc	x+e=x
blank	abc	=A1>B1	blank	e>x=e
blank	abc	=B1>A1	blank	x>e=e

  Valid Addresses

There are two places we use addresses: in the address field and in the cells with formulas. When we get a “real” (graphical) interface, the address will mostly be implicit. But even so, we’ll test it here just to be safe.

Let’s introduce a new fixture, Address. It will be a ColumnFixture: we’ll put address in one column, valid() in another, and standardized() in another. (A programmer will have to write the new fixture for us.)

The rules are: a valid address is a letter (A-Z, a-z) followed by one or more digits (0-9). Case is ignored. Leading 0s are ignored. “0” is not a valid row number.

Address
address	valid()	standardized()
A1	true	A1
a1	true	A1
A9874	true	A9874
Z1	true	Z1
z1	true	Z1
Z3992	true	Z3992
z3992	true	Z3992
AA393	false
zX202	false
é17	false
1	false
~1	false
~D1	false
y&1	false
^	false
X392%	false
H001	true	H1
j00010	true	J10
e000	false
A0	false
z0	false

Let’s make sure that case-insensitivity works in formulas:

SpreadsheetFormula
a1	b1	b1()
abc	=A1+a1	abcabc

Formula Errors

If a formula contains an error, we’d like it to display as “#error.” We’ll put all the invalid names from the previous table into formulas, and verify that formulas behave correctly. Then we’ll try various improper combinations of operators.

fit.ActionFixture
start	Spreadsheet		Create a new spreadsheet.
enter	a1	=AA393	Bad address
check	a1	#error	Marked as error
check	formula	=AA393	Formula as written
enter	a1	=A2	Change to valid address
check	a1		Make sure #error is cleared

SpreadsheetFormula
a1	a1()	Comment
=zX202	#error	Two letters
=é17	#error	Non-ASCII
=1	#error	No letters
=~1	#error	No letters
=~D1	#error	Unacceptable character
=y&1	#error	Extra character
=^	#error	No letters/digits
=e000	#error	Too many digits
=A0	#error	Invalid row #
=z0	#error	Invalid row #
=	#error	Missing formula

Then we’ll get to some operators:

SpreadsheetFormula
a1	a1()	Comment
=’A2	#error	‘  should be postfix
=’A2′	#error	Can’t be before and after
=A2+	#error	Need other term
=A3+A4+	#error	Need other term
=A2++A3	#error	Missing term
=A2+’+A3	#error	‘ isn’t a term
=A2”’+A3	blank	OK to mix things
=A2)	#error	Missing (
=(A2	#error	Missing (
=((((((((((((A2))))))))))))	blank	OK – big expression
=((((((A2+(A3))))+A4)	#error	Unbalanced – too few )
=(((A2>A3	#error	Unbalanced – too few )
=(A2>A3)))	#error	Unbalanced – too many )
=A2>A3>	#error	Can’t trail >
=A2>A3>A4	#error	Can’t repeat >

Loops

If a formula uses itself (directly or indirectly), we don’t want it to loop forever trying to figure it out. Instead, we’d like the display to be “#loop.”

SpreadsheetFormula
a1	b1	c1	d1	e1	a1()	e1()
=A1	blank	blank	blank	blank	#loop	blank
=B1	=C1	=F1+D1	=E1	no-loop	no-loop	no-loop
=B1	=C1	=F1+D1	=E1	=A1	#loop	#loop

Conclusions

This paper has demonstrated a set of tests using the fit acceptance testing framework. Some things to note:

• The tests here have been written as if a customer specified them, without much demonstration of the programming cycle. But programmers can work with these tests in much the way they would with JUnit.
• The tests are written without benefit of the feedback of a working system. (I wrote just enough code to make the first test not throw an exception.) When I went back to implement the system, I found a number of bugs in the tests.
• The tests look at only part of the system: the core functionality. There are other aspects of a real application that we aren’t testing. (For example, it may be non-trivial to connect a screen to the core code.)
• Even a small application such as this requires a fairly large set of tests. With more programming work on the fixtures, we might be able to reduce some of the noise. Real applications will organize tests into multiple files, and will have to pay more attention to the challenges of consistency, test independence, and feature interaction.
• It feels smooth to mix light natural-language specification with formal, executable tests.
• Fit has a number of features we haven’t used.

I’ve heard that many teams use xUnit for unit testing, but still struggle to get customer tests before or even after stories are implemented. I hope frameworks such as fit can help lower the barriers to doing this crucial task.

Resources and Related Articles

• https://fit.c2.com
• Acceptance Tests for a Query System
• Acceptance Test Mechanisms

[Written April 20, 2003; revised April 26, 2003, to correct mis-stated identity & in response to Ward Cunningham’s great suggestions about improving the fixtures. Revised May 1, 2003 to fix some test problems. 2012 – the WordPress version is designed to simulate the original look.]