by
Mario Aquino, Principal Software Engineer
Object Computing, Inc. (OCI)

Introduction

Every few years, someone in the tools and practices community has a great idea for improving the process of software development; one that is important enough for anyone with a role in software development to stop and take notice. Fit (Framework for Integrated Tests - http://fit.c2.com) is a tool for expressing application acceptance tests using tables, and one that solves a fundamental need in software development: capturing business rules in an easily accessible and executable form.

Acceptance tests are tools for exercising the business rules of an application to observe that their implementation meets a customer-defined expectation. Ideally, these tests are automated and interact directly with an application. However, often acceptance tests are simple documents that "script" a series of steps a human tester follows to determine if an application is behaving correctly according to business rules. Fit's approach to testing uses tables (from HTML files or other formats such as Microsoft Excel spreadsheets) as a way to organize assertions about the business rules an application is meant to enforce. These tables can use regular business terminology to clearly convey the intent of the test in language familiar to the customer. In fact, the greatest advantage of this simple table-driven approach is that tests can be written by the customer, if not in collaboration between the customer and developers. Once they are read by the framework, the tables drive special components, called fixtures, that interact with the application under test (whether it be Swing, web-based, or command-line driven) and observe outcomes that are defined by business rules.

Fixtures

Fit fixtures are Java classes that extend from the fit.Fixture base class and come in three varieties: ColumnFixtures, RowFixtures, and ActionFixtures. ColumnFixtures are meant to be used in tests that focus on performing a calculation based on series of variable inputs. RowFixtures are ideal for evaluating the state of a set of domain objects to test whether they contain expected values. ActionFixtures capture a sequence of interactions with a "device" that represents the interface to the application under test.

The remainder of this article will focus on demonstrating Fit via example by capturing some of the business rules for a banking application in a series of acceptance tests.

A Simple Banking Application

The software needed to manage the customers and accounts of the First National Piggy Bank is simple and straightforward. The bank has customers and customers can have any number of accounts that they use to hold and access their money. Funds can be deposited, withdrawn, or transfered in between accounts of the same customer.

Customer Name Business Rules

Let's start off by defining tests for the business rules of a bank customer. As far as the bank is concerned, customers are identifiable by name. In order for a customer to be tracked by the system, the customer's name must be known. For this business rule we create a table and ColumnFixture called "ValidateCustomerName".

This simple table sets the conditions for testing business rules. The cell in the first row of the table identifies the fixture class that Fit should look for when it tries to run this test. At test execution time, Fit will create an instance of the ValidateCustomerName fixture class and for each row in the table, pass whatever value is specified in the customer name column to a field in the ValidateCustomerName instance, call the valid() method in that instance and compare what is returned from that method with what appears in the cell for that row and column.

The code for the ValidateCustomerName fixture is equally simple.

import jnb.Bank;

public class ValidateCustomerName extends fit.ColumnFixture {
    private Bank systemUnderTest = new Bank();
    public String customerName;

    public boolean valid() {
        systemUnderTest.addNewCustomer(customerName);
        return true;
    }
}

This class extends fit.ColumnFixture and defines a public String field customerName as well as a method valid(), which correspond to the two column headings in the second row of the table shown above. All ColumnFixture tables follow the same pattern:

• The first column of the first row of the table specifies the Fixture class that will be used to the execute the table at runtime.
• The second row of the table defines public fields and methods from the Fixture class for the table. Fit determines whether columns in the second row represent fields or methods in the target fixture class by the existence of parentheses '()' at the end of the text string.
• Separated words in the second row of the table must be matched by camel-cased fields and methods in the Fixture class. In the above table, customer name corresponds to the customerName public field in the ValidateCustomerName class. The table could also use customerName as the column heading or CustomerName() (in which case, the public field would be replaced by a public method of the same name in the fixture code), but these seem less "readable" and more code-like which doesn't always appeal to customers.
• Fit ignores any formatting applied to table cells; italicized, bold, or underlined text can be used to highlight important rows or values in the table without affecting Fit's ability to execute the test.

Fit executes tests one table row at a time, from left to right column order. According to the first test values row in the ValidateCustomerName table, Fit will pass an empty (null) value to the customerName field, call the valid() method, and expect the method call to error (throw an Exception of some kind). error is a special keyword in Fit; when used in a method call column it tells Fit to expect an exception to be thrown. The absence of an exception thrown by the method causes a comparison failure for the cell (the cell appears red instead of green in the test report).

Running Fit tests

Fit tests can be run using the fit.FileRunner class, which expects a path to the test file and a path name for a file it will create for the test report.

java -cp fit.jar;. fit.FileRunner <input_test_path> <output_report_path>

When the test for this table executes, the cells representing expected outcomes are shaded green, red, yellow, or gray; green means that expected and actual values matched, red means they didn't match (in which case expected and actual appear in the cell), yellow indicates that an unexpected error/exception was thrown (a stacktrace appears in the cell), and gray means that the field or method is not implemented in the Fixture class or that the cell was ignored by Fit.

null appears in the first test cell below, even though the cell in the test table was blank. Fit implicitly uses the last value of a public fixture field if no value is specified for the executing test row in the test table. When this happens, Fit displays the implicitly used input value as shaded text in the test report table. Since the first input cell in the test table was blank, there was no previous value for the customerName field, so null was used.

Adding Bank Customers

Next, let's focus on the business rules for adding customers to the banking system. Adding a new customer includes entering their name and creating any number of accounts and starting balances. The system needs to keep track of all accounts established for a customer as well as calculate the cumulative (total) balance for all accounts belonging to the customer. We could specify rules for interest bearing accounts or accounts that require a minimum balance to avoid a penalty, but for this example the rules will be kept simple.

The process of adding customers and creating their accounts follows a sequence of steps that we will capture using another type of fixture called an ActionFixture. Unlike the ColumnFixture where series of inputs and expected outputs are grouped together by columns, the ActionFixture tables are supposed to represent a sequence of interactions with a metaphorical "device", which represents the interface to the system under test. ActionFixture tables support four kinds of interactions, specified by the keywords start, enter, check and press.

The start keyword tells the framework to create an instance of the Fixture class specified in the second cell of the second row of the table (CustomerBankingActions, above). enter, check, and press correspond to write (to a field or method), read (from a field or method), and call (methods with no return value) operations on the instance created by the start. In ActionFixture tables, each check will result in a comparison of the value specified in the third cell of the row with the value of the field or method matching the name in the second cell of the row.

import jnb.Account;
import jnb.Bank;
import jnb.Customer;
import jnb.Money;

import java.util.Collection;

public class CustomerBankingActions extends fit.Fixture {
    private Bank systemUnderTest;
    private Customer customer;
    private String accountID;
    private Money startingBalance;

    public void customer(String customerName) {
        this.customer = getCustomer(customerName);
    }

    private Customer getCustomer(String customerName) {
        final Bank bank = getSystemUnderTest();
        final List customerList = bank.getCustomers(customerName);
        if (customerList.size() == 0) {
            return bank.addNewCustomer(customerName);
        }
        return (Customer)customerList.get(0);
    }

    public Account[] accounts() {
        final Collection accounts = customer.getAccounts();
        return (Account[])accounts.toArray(new Account[accounts.size()]);
    }

    public void account(String accountID) {
        this.accountID = accountID;
    }

    public void startingBalance(Money money) {
        this.startingBalance = money;
    }

    public void createAccount() {
        this.getSystemUnderTest().addCustomerAccount(customer, accountID, startingBalance);
    }

    public Money customerTotalBalance() {
        return this.customer.getBalance();
    }

    public Object parse(String s, Class type) throws Exception {
        if (Account.class.isAssignableFrom(type)) {
            return customer.getAccount(s);
        } else if (Money.class.isAssignableFrom(type)) {
            return new Money(s);
        }
        return super.parse(s, type);
    }

    private Bank getSystemUnderTest() {
        if (systemUnderTest == null) {
            systemUnderTest = TestBank.systemUnderTest == null ? new Bank() : TestBank.systemUnderTest.bank;
        }
        return systemUnderTest;
    }

    public void transferFrom(Account transferFrom) {
        this.transferFromAccount = transferFrom;
    }

    public void transferTo(Account transferTo) {
        this.transferToAccount = transferTo;
    }

    public void transferAmount(Money amount) {
        this.transferAmount = amount;
    }

    public void transactTransfer() throws InsufficientFundsException, InvalidTransactionException {
        this.transferToAccount.transferFunds(transferFromAccount, transferAmount);
    }
}

There are a number of details from the implementation of the CustomerBankingActions fixture that merit explanation. Unlike the ValidateCustomerName class that must descend from fit.ColumnFixture, CustomerBankingActions extends the base fixture class fit.Fixture (rather than extending fit.ActionFixture as one might expect). fit.ActionFixture interacts with other Fixture instances via the enter, check, and press operations. The actor (the class specified in the cell after the start) must be a subclass of fit.Fixture because ActionFixture needs to access an overridden method called parse() to handle type conversion for values specified in table cells.

For example, the first check operation in the CustomerBankingActions table is supposed to compare the value "$0.00" with whatever is returned by a method called customerTotalBalance(), which Fit expects to find in the CustomerBankingActions class. According to the code above, that method returns an object of type jnb.Money, which is a domain class from the bank application. Behind the scenes, Fit uses reflection on the CustomerBankingActions class to find the customerTotalBalance() method and queries the class of its return type. Next Fit calls parse() on the actor for this table, passing in the String value from the table cell (in this case "$0.00") and the class of the return type of the customerTotalBalance() method (jnb.Money). The Money object returned by parse() is compared via its equals() method with whatever is return by the customerTotalBalance() method; if the two are equal, the comparison succeeds and the cell appears green in the test report,

otherwise the cell will be red and display both the expected and actual values determined at runtime.

The real power of this capability is in allowing Fit tests to utilize domain objects from the application under test, enabling complex equality comparisons in a single step. Here is the same table from the test report:

In addition to handling arbitrary types, Fit also supports arrays of objects. The accounts() method in CustomerBankingActions returns an array of Account objects, which are expressed in the test table as a series of values separated by commas (see the last check accounts in the test table).

Performing Account Transactions

As a final example, let's look at a third type of fixture, the RowFixture, as well as how to combine multiple tables in a single test. A test to exercise the business rules of standard deposit, withdrawal, and transfer transactions is needed. Those rules are as follows:

• Account deposits must be in amounts (money) greater than $0.
• Withdrawal amounts must not be greater than the balance in the account from which money is being withdrawn.
• Fund transfers can only be done between two accounts belonging to the same customer and amounts must adhere to the rules established for deposits and withdrawals.

Failure of any of these business rules must leave the account in its initial (pre-transaction) state with regard to its balance.

The following series of tables are all part of the same test. Some cells appear shaded because the tables are from the report generated after the test run. Test tables are executed in the order in which they appear in the file.

Some Fit tables can share the state of their fixtures with each other; ActionFixture tables can use the actors created by other tables within the same test (as is seen in tables 2, 5, and 8 below). The first two tables setup conditions for the rest of the test by creating a utility fixture called TestBank that will hold a reference to a jnb.Bank object used by other fixtures in the test, then creating a CustomerBankingActions fixture and using it to add a bank customer and account to the system.

1. Setup the system

2. Create a customer with a checking account

3. List all accounts in the bank
This next table uses a RowFixture to compare a list of domain objects from the banking application against values expected by the test. The code for the CustomersAccountList fixture shows two required facets of RowFixtures, a Object[] query() method for returning the set of domain objects that will be compared to rows in the table, and a Class getTargetClass() method that tells Fit the type of object that will be returned by query() (in this case, instances of an inner class called BankAccount). As with all other types of fixtures, Fit is able to compare values from table cells with instances of application domain objects because CustomersAccountList implements a parse() method, which is responsible for converting String values into objects of a particular class. The column headings (from the second row) in the CustomersAccountList table refer to public fields in the target class (BankAccount) for this RowFixture. Behind the scenes, Fit uses reflection on the class reference returned by getTargetClass() to determine the class type for each of the columns in the RowFixture table.

Though it may seem awkward to expose public fields in a class, fixtures exist to connect tables to the system under test and are not themselves actually part of the real application. The column headings id, customer and balance appear as public fields (of type String) in the CustomersAccountList.BankAccount class, but they could just as easily have been methods, in which case the table would refer to them as: id(), customer() and balance(). As well, BankAccount need not have been an inner class of the CustomersAccountList class but rather a top-level class (or even an interface - in which case the public fields would have to have been methods).

At this point, the bank only has one customer. This list appears again (with two customers) at the end of step 8 in this test.

import jnb.Account;
import jnb.Customer;
import jnb.Money;

import java.util.*;

public class CustomersAccountList extends fit.RowFixture {
    public Object[] query() throws Exception
    {
        final List customers = TestBank.systemUnderTest.bank.getCustomers();

        return getBankAccounts(customers);

    }

    protected Object[] getBankAccounts(final List customers)
    {
        List bankAccounts = new ArrayList();
        for(Iterator iter = customers.iterator(); iter.hasNext(); ) {
            Customer customer = (Customer) iter.next();
            final Collection accounts = customer.getAccounts();
            for(Iterator accountsIter = accounts.iterator(); accountsIter.hasNext(); ) {
                final BankAccount bankAccount = new BankAccount((Account)accountsIter.next());
                bankAccounts.add(bankAccount);
            }
        }

        return bankAccounts.toArray();
    }

    public Class getTargetClass()
    {
        return BankAccount.class;
    }

    public Object parse(String s, Class type) throws Exception
    {
        if (Money.class.isAssignableFrom(type)) {
            return new Money(s);
        } else if (Customer.class.isAssignableFrom(type)) {
            return new Customer(s);
        }
        return super.parse(s, type);
    }

    public static class BankAccount {
        public final String id;
        public final Customer customer;
        public final Money balance;

        public BankAccount(Account account)
        {
            this.id = account.getId();
            this.customer = account.getCustomer();
            this.balance = account.getBalance();
        }
    }
}

4. Check rules that prevent zero-value deposits as well as maintain the original account balance after an invalid transaction
The Deposit table is implemented as a ColumnFixture. A link to the source code for this fixture, the application classes, and all HTML files for this article can be found in the resources section of this article.

5. Create a savings account, then transfer money from checking to savings
This ActionFixture table implicitly uses the same actor (CustomerBankingActions) from the last ActionFixture table (#2 above).

6. View all account details for Sam Walton
This RowFixture table is a variation from the CustomersAccountList table (#3 above). That table dealt with all customers in the system, but this table provides the name of a specific customer, demonstrating how tables can pass parameters to their fixture implementations in cells appearing after the fixture name. The implementation of CustomerNameAccountList shows how the parameters passed by the table are accessed in the fixture via the args array inherited from fit.Fixture.

public class CustomerNameAccountList extends CustomersAccountList {

    public Object[] query() throws Exception
    {
        return getBankAccounts(TestBank.systemUnderTest.bank.getCustomers(args[0]));
    }
}

7. Check rules that prevent withdrawal of more funds than appear in the account
The Withdrawal table (like the Deposit table) is implemented as a ColumnFixture.

8. Create a second customer and confirm that transferring money between accounts from different customers is not allowed
The last press operation in this table is shaded in yellow and shows a stack trace from an exception thrown because the funds transfer attempt broke the business rule enforced by the system.

jnb.InvalidTransactionException: Cannot perform transfers between different customers
	at jnb.Account.transferFunds(Account.java:81)
	at CustomerBankingActions.transactTransfer(CustomerBankingActions.java:88)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:324)
	at fit.ActionFixture.press(Unknown Source)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:324)
	at fit.ActionFixture.doCells(Unknown Source)
	at fit.Fixture.doRow(Unknown Source)
	at fit.Fixture.doRows(Unknown Source)
	at fit.Fixture.doTable(Unknown Source)
	at fit.Fixture.interpretFollowingTables(Unknown Source)
	at fit.Fixture.interpretTables(Unknown Source)
	at fit.Fixture.doTables(Unknown Source)
	at fit.FileRunner.process(Unknown Source)
	at fit.FileRunner.run(Unknown Source)
	at DirectoryRunner$MyFileRunner.main(DirectoryRunner.java:55)
	at DirectoryRunner.runTestsInDirectory(DirectoryRunner.java:32)
	at DirectoryRunner.main(DirectoryRunner.java:15)

  

This last table verifies that all the account balances match what they were before the failed funds transfer.

Notes and Closing

Fit is released under the Gnu Public License (GPL) and has already been extended by two notable projects (that are themselves also open source): FitNesse, which is a Wiki-based Fit execution server, and FitLibrary which adds useful fixtures (the DoFixture) and utilities (support for Microsoft Excel spreadsheet-based Fit tests and running all tests in a directory hierarchy). Fit was originally written in Java, but has been ported to many other programming languages including C++, dotNet, Perl, Python, and others.

This article has attempted to use a simple example to illustrate how to use Fit to test application business rules. The sample application had no user interface, in fact the authors of the framework recommend business rules testing that doesn't interact with the system via the user interface but rather writing test fixtures that make direct calls into application entry points. The reasoning is that frequent UI changes might make acceptance tests fragile or force the tests to follow whatever interaction sequence is provided by the UI thereby making the tests less concise. There is a lot of merit to these arguments, as is there to the notion that true acceptance testing exercises the entire application in the same way that a user might to ensure that all application behaviors (and the business rules they enforce) are externally observable from the user interface. Open source tools like Jemmy (for interacting with Swing user interfaces) and jWebUnit (for interacting with web user interfaces) simplify the UI interaction layer for acceptance tests; test fixtures can use these kinds of utility libraries to drive the running application without needing to "expose" APIs that side-step the user interface.

Whether Fit tests interact with an application user interace or programming interface, they are by nature table-driven and business rules focused. Among the great benefits of this approach is that the tests can be authored if not extended through cooperative effort between customers and developers. This collaboration comes via conversations and perhaps "pair-programming" sessions with customer representatives and software developers sitting side-by-side discussing the business rules of the application. In this way, Fit is as much a facilitator of understanding between members of the same team as it is a way to clearly and objectively capture how an application should behave.

References

• Source code (including banking classes, fixtures, and html tests) from this article
• Fit - http://fit.c2.com
• Fit for Developing Software - by Rick Muckridge, Ward Cunningham (Published June 29, 2005 - ISBN 0321269349)
• FitLibrary - http://fitlibrary.sourceforge.net/ (download from Sourceforge)

Mario Aquino would like to thank Lance Finney and Tom Wheeler for providing valuable feedback in their reviews of this article.

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IT阅读于2006年3月25日 上午06时50分35秒发布 #