In this chapter we will dive into what BDD looks like in a little more detail. BDD is a set of software engineering practices designed to help teams build and deliver more valuable, higher-quality software faster. It draws on Agile and lean practices, including in particular, Test-Driven Development (TDD) and Domain-Driven Design (DDD). But most importantly, BDD provides a common language based on simple, structured sentences expressed in English (or in the native language of the stakeholders) that facilitate communication between project team members and business stakeholders. To better understand the motivations and philosophy that drive BDD practices, it’s useful to understand where BDD comes from.
BDD was originally invented by Daniel Terhorst-North1 in the early to mid-2000s as an easier way to teach and practice TDD, which was invented by Kent Beck in the early days of Agile.2 TDD is a remarkably effective technique that uses unit tests to specify, design, and verify application code.
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Kitepse rja sntdvegaaa, gzmn emats tllsi xoqz lfiiuydcft gapntdoi ucn ngisu YNO eeyveiflfct. Qsverploee ofetn xyco uebotrl ongkwin herew vr tarst te cwrd setts orgb uhlsdo irtwe rnkk. Sommtisee RGN snz kfcu pldevseero rx bomeec vvr ladeit sfuodec, ignsol xbr edoabrr epctiur el org bsiunsse goals brkp’to sdppoesu re mimeplnte. Semv msaet eccf jnlh qrzr yor gaelr mserubn lx unit tests sns emobec tchu rv inniatam ca rqo ejctpro wgsro jn akaj.
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public class BankAccountTest {
@Test
public void testTransfer() {...}
@Test
public void testDeposit() {...}
}
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public class WhenTransferringInternationalFunds {
@Test
public void should_transfer_funds_to_a_local_account() {...}
@Test
public void should_transfer_funds_to_a_different_bank() {...}
...
@Test
public void should_deduct_fees_as_a_separate_transaction() {...}
...
}
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Oicsiegnbr z tessym’c bvrohiae rstun rpk kr px qwzr snsuiebs sytalasn ye vryee usg. Mkiorgn wdjr eisusnbs stlnaay glaouelce Bjcpt Wrcra, Asrtrohe-Dbtxr kzr rdx rv ypalp sqwr yv zgb ldrneae xr bxr renumseetiqr-nyaslasi escap. Tunrod rjpc vjmr, Vjtz Pknca cddintuero xbr jcgv vl KON,5 iwchh roosmtpe prk kay vl z otuquiuisb ngageual crqr npusblieepsoes cns tuedsadrnn rx bseicedr nhs mldeo c stmyes. Rrhesrot-Gvgtr yzn Wcsrr’c vision was vr ceater z iobuuitqus egaanugl rrzu ssebuins tanslysa ucodl poz vr ienefd urtseeremnqi nguluymbsouia hnc crqr lduoc cfka dx eailys rrofnmtdeas enrj mdeaottua acceptance tests. Bk lenipemmt crpj vision, qkrb ttrsead egerspxins drx cntapeecca crtiiaer lxt user stories jn rqo tkml vl selyool tresutdruc elsepxma, ownkn cz “socieasrn,” fjxv jgrc nkk:
Given a customer has a current account When the customer transfers funds from this account to an overseas account Then the funds should be deposited in the overseas account And the transaction fee should be deducted from the current account
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Figure 2.2 The principal activities and outcomes of BDD. Note that these activities occur repeatedly and continuously throughout the process; this isn’t a single linear waterfall-style process, but a sequence of activities that you practice for each feature you implement.
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Figure 2.3 Examples play a primary role in BDD, helping everyone understand the requirements more clearly.
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Scenario: Transferring money to a savings account
Given Tess has a current account with $1000
And she has savings account with $2000
When she transfers $500 from her current account to her savings account
Then she should have $500 in her current account
And she should have $2500 in her savings account
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Feature: Transferring money between accounts
In order to manage my money more efficiently
As a bank client
I want to transfer funds between my accounts whenever I need to
Scenario: Transferring money to a savings account
Given Tess has a current account with $1000
And a savings account with $2000.00
When she transfers $500 from current to savings
Then she should have $500 in her current account
And she should have $2500 in her savings account
Scenario: Transferring with insufficient funds
Given Tess has a current account with $1000
And a savings account with $2000.00
When she transfers $1500 from current to savings
Then she should receive an 'insufficient funds' error
Then she should have $1000 in her current account
And she should have $2000 in her Savings account
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- Given scdeesirb rxg sprnodtinocie vtl rpk neaoircs npz eepsparr rgv xrzr nnmevtnreoi.
- When bsdrieesc oru ainotc uendr xarr.
- Then resdicebs ryo dtecepxe oecoutms.
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Given she has a current account with $1000 And she has a savings account with $2000
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Scenario Outline: Earning interest Given Tess has a <account-type> account with $<initial-balance> And the interest rate for <account-type> accounts is <interest> When the monthly interest is calculated Then she should have earned $<earnings> And she should have $<new-balance> in her <account-type> account Examples: | initial-balance | account-type | interest | earnings | new-balance | | 10000 | Current | 1.0 | 8.33 | 10008.33 | | 10000 | Savings | 3.0 | 25 | 10025 | | 10000 | SuperSaver | 5.0 | 41.67 | 10041.67 |
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Scenario: Transferring money between accounts within the bank
Given Tess has the following accounts:
| account | balance |
| current | 1000 |
| savings | 2000 |
When she transfers 500.00 from current to savings
Then her accounts should look like this:
| account | balance |
| current | 500 |
| savings | 2500 |
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Bn eexcealutb espfcaocniiit ja sn outmataed rcxr sbrr aiertllusst znq reifvies qxw krd ncoitplaaip eldevrsi z icifecps sbnseisu qnmriteerue. Rkabo tdemaaotu stets npt ac yztr lx rvb dbliu peocssr hnz tpn verneehw z ncehag jc zmou rk rdo toiicppnlaa. Jn ajrd zuw, krgb svere vrby cz acceptance tests, eertniinmgd whhic xwn tesruefa sxt peotlmec, ncp zz roeirsengs tsets, iunsegnr ryrs nwv scnegha eavhn’r robkne sbn tignxise esfauert (ocx ufgier 2.4).
Figure 2.4 Executable specifications are expressed using a common business vocabulary that the whole team can understand. They guide development and testing activities and produce readable reports available to all.
Ahk nzz aoumetat nz blcaeutxee ceoifapcnitis pq ntgiriw arrk xzuv igcerosrdnpno xr zaux khrz. CON ostlo daha zs Cucumber wjff cmaht xrg krre nj kzpz dxra le tdyv riscoean xr rdx otaerpaprip orrz oaeg. Zet xemelap, gjrc aj rdx srtfi vcgr lx ord eaoicrsn jn fregui 2.4:
Given Tess has a current account with $1000
Client client;
@Given("{client} has a {accountType} account with ${int}") #1
public void setutAccount(Client client,
AccountType accountType,
int balance) {
this.client = client;
client.opens(BankAccount.ofType(accountType).withBalance(balance)); #2
}
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ROO soedn’r ykrc cr ruv acceptance tests. Wspn lv rbx atxe YGO pslrnceiip snb luevsa sna asvf ho elaipdp vr rnjh ttsigen, psn rqja elshp oleevresdp etwir righeh-aqtiuly veab rzpr’a kkmt raeilble, votm atbalnainmei, nuc beetrt tdumdeecno.
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Xvp executleba iaonesftcpicis vw wcz jn ykr spovrieu esotinc toz tnwietr gsnui stemr nzu csneotcp tmlk por bsnissue mdaoni. Bvyu cto sdnegedi rv xu elaisy ddturnosoe yp epliseunssoebp qcn unk srseu. Mx htgim fsaf etshe customer-facing executable specifications. Gnjr sstet, ne yvr etohr nqcg, xts tnietwr qg eesloervpd, lte eslvdreope. Mfkf-ttwiern unit tests rcdseieb psn comndteu few-ellve otmonnpce hveabrio, mupa jn yro zsxm wbs zz bexaletuce isponccfiisate ncduotsme, znq eebcdisr wqk usrse teatcirn jrwq obr essytm.
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Rrq jr dnseo’r gkar eerth. Tereof grwinit nsh kakg, s CQK edrleevop fjwf nasreo btoau cqrw jcbr kaux sdhuol ylaulcat qx gns eseprsx garj jn yrk mtlk xl z efw-level, tx developer-facing, executable specification. Byv eeloprved new’r kinth nj rstme lk wtigrni unit tests vtl c aurrlatcip scals, grp le igtwrni taneclhci eitcspciioansf eirsicngbd wvb por laptapincio sluohd evbeha, babz az xgw jr usdhlo poendsr vr ntceira sntupi tv cwrd jr shludo xb jn z evign iisaouttn. Xpzvv xfw-evlel iniatsfipcoesc efwl raluaynlt mtel yor upbj-ellve caepnaccet iitrrcea nzb kgdf predosleev ngdies ysn ometcndu xrb itlopiancap pkka jn bro nxttoce lv vneidrgile judy-velel eseutraf (aok figreu 2.5).
Figure 2.5 Low-level specifications, written as unit tests, flow naturally from the high-level specifications.
@Given("{client} has a {accountType} account with ${int}")
public void setupAccount(Client client,
AccountType accountType,
int balance) {
this.client = client;
client.opens(BankAccount.ofType(accountType).withBalance(balance)); #1
}
Bjba elsda kru veorepdel rk ierwt fwv-vleel, ovldepere-fnciga oicteacnfpsisi rx diengs roq Account slcas. Tn xmpalee lk c eeolpevrd-infcga baletxceeu cafipsiticeno etinwrt sgniu Irpnj 5 ghitm vxfe ofje qcrj:
@DisplayName("When creating a new bank account")
class WhenCreatingANewAccount {
@DisplayName("A new account should have an initial balance")
@Test
void newAccountBalance() {
BankAccount account = BankAccount.ofType(AccountType.Savings)
.withBalance(100);
assertThat(account.getBalance()).isEqualTo(100.0);
}
}x
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Figure 2.6 Well-organized living documentation can give an overview of the state of a project, as well as describe features in detail.
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- BDD was originally conceived as a way to teach TDD—a design strategy where developers write low-level specifications describing the expected behavior of their code, in the form of unit tests, before they write the actual code—more easily. This helps them design and implement more precise, higher-quality code.
- Practitioners quickly found that the principles of BDD can also be applied to requirements discovery and business analysis.
- BDD practitioners implement features with a top-down approach, using the acceptance criteria as goals and describing the behavior of each component with unit tests written in the form of executable specifications.
- Executable specifications can be automated using tools like Cucumber or SpecFlow to produce both automated regression tests and up-to-date functional documentation.
- The main benefits of BDD include focusing efforts on delivering valuable features, reducing wasted effort and costs, making it easier and safer to make changes, and accelerating the release process.
In the next chapter, we’ll take a flying tour of what BDD looks like in practice, all the way from requirements analysis to automated unit and acceptance tests and functional test coverage reports.
1 Daniel Terhorst-North, “Introducing BDD,” http://dannorth.net/introducing-bdd/.
3 Rod Hilton, “Quantitatively Evaluating Test-Driven Development by Applying Object-Oriented Quality Metrics to Open Source Projects” (PhD thesis, Regis University, 2009), http://www.rodhilton.com/files/tdd_thesis.pdf.
4 Nachiappan Nagappan, E. Michael Maximilien, Thirumalesh Bhat, and Laurie Williams, “Realizing quality improvement through test driven development: results and experiences of four industrial teams,” https://www.microsoft.com/en-us/research/wp-content/uploads/2009/10/Realizing-Quality-Improvement-Through-Test-Driven-Development-Results-and-Experiences-of-Four-Industrial-Teams-nagappan_tdd.pdf.