Testing Business Logic begins in Requirements Paul Vincent

BCS SIGiST – Summer 2015 Conference - Friday 5 June 2015

Some Known Best Practices … • Agile development (fail early, deliver often) • Test-driven development (test specification = system specification) • Model-driven development (formal models are more easily transformed into software)

Ref: BCS SIGiST Spring 2015

Ref: BCS SIGiST Winter 2014

BCS SIGiST Autumn 2014

1. Why Test in Requirements?

Ref: http://loadstorm.com/2011/10/cost-fixing-software-defects/

2. But how can Requirements be Formal? Decision

• Models can be formal • Example = BPMN process • Can be validated, simulated, loops detected etc

Gateway

Task

Ref OMG DMN

3. Decision Models for Requirements • Decision “models” are not new!

Babylon 1800BC - Mathematical look-up table

3. Decision Models for Requirements • Decision “models” are not new!

4. Decision Models for Testing 1977

5. Decision Models as Requirements • How can we define a formal model for business logic that Business Analysts can use? With appropriate notation, methodology and standards?

• Can modelling tools embed appropriate testing to automate tests?

Decision Methodologies • TDM - The Decision Model (von Halle, Goldberg) • Published, commercially supported, specific notation • Tooling (BiZZDesign, Sapiens, SAP,…)

• DTM - Decision Table Methodology (Vanthienen) • Published across papers and books, commercially supported • Tooling (Various) for decision tables

• Decision Management Systems Methodology (Taylor) • Published, commercially supported • Own tooling (Decision Management Solutions)

Decision Notations • TDM - The Decision Model (von Halle, Goldberg)

• Published, commercially supported, specific notation • Tooling (BiZZDesign, Sapiens, SAP,…)

• OMG DMN - Decision Model and Notation

• Published, commercial support starting, specific notation • Tooling (Signavio, DMS, FICO, …)

Case Study: Example using TDM Determine Policy Renewal Method

Manual or Automatic

Manual Renewal

Automatic Renewal

A. What is Decision? • Find Manual or Automated status… TDM BPMN Determine Policy Renewal Method

Per OMG DMN • A Decision is the act of applying decision logic to one or more inputs to produce one output • A Decision Logic is a formal expression that defines the output of a decision with respect to its inputs • A decision logic can be a Computation • Or a Fixed Alternatives Ruleset, represented as a Decision Table or a Decision Tree • Or it can be an Imported Formulation (e.g. a predictive model in PMML)

B. What is the Decision Logic

Decision Table / Rule Family describing logic AND

OR

CONCLUSION

FAMILY OF RELATED BUSINESS RULES

C. Is this complete, no duplications etc? ALL VALUES TESTED?

ALL VALUE COMBINATIONS TESTED?

ALL CONCLUSIONS CONSISTENT?

Verify Rule Family / Decision Table (static test)

D. Does this do what is intended? ARE THE RESULTS AS EXPECTED AGAINST TEST CASES?

Validate Rule Family / Decision Table (test cases)

Validate Rule Family / Decision Table (test cases)

Validate Rule Family / Decision Table (test cases)

Validate Rule Family / Decision Table (test cases)

Validate Rule Family / Decision Table (test cases) TEST CASES CREATED, CUSTOMISED, ETC

Validate Rule Family / Decision Table (test cases) TEST RESULTS SHOWN

Validate Rule Family / Decision Table (test cases) TEST CASE SHOWN IN DECISION TABLE / RULE FAMILY

E. Unit Testing Done REPEAT EXHAUSTIVE TESTS FOR THESE RULE FAMILIES

F. Test Connections to Rule Families

DEFINE TESTS FOR ALL BRANCHES, TESTING EACH LINK

Assumptions for decision modelling for testing 1. I know the decision I need to make (may be re-used across processes) 2. I define a formal / rigorous data model too (name, type, value domain, single/list) • See Data Modelling for Requirements Testing presentation at some future SIGiST!

For Business Logic requirements… 1. We can model business logic using Decision Models

For Business Logic requirements… 1. We can model business logic using Decision Models 2. We can verify the completeness + uniqueness of this business logic

For Business Logic requirements… 1. We can model business logic using Decision Models 2. We can verify the completeness + uniqueness of this business logic 3. We can validate the business logic against all possible use cases for each rule family + all links in a decision model of multiple rule families

How useful is this? • Example 1: a product selection requirement • Original analysis = 15,000 rows of business logic in Excel • Decision Modelled = ~220 rows across ~18 decisions by 6 Business Analysts over 2-3 weeks

How useful is this? • Example 2: business loan compliance with policy • Original analysis = spreadsheet of X tabs of metrics vs business sector vs threshold levels

• Decision Modelled = Validate-able thresholds vs policies, Side by side comparison of thresholds, Champion challenger etc

Standards to support this pattern? • Standardisation effort by OMG DMN • Notation and metamodel • Can be used with multiple methodologies eg DTM, TDM

• Tooling to support DMN underway

DMN Decision Requirements Diagram

INPUT

DECISION

BUSINESS KNOWLEDGE MODEL

TDM / DMN

=

DRD Key

DRD Connections Guide

Decision Table (a Business Knowledge Model)

Decision Table Hit Policies Indicator Indicator Description Term Single Hit

Multi Hit

U

Unique

Only 1 rule matched

A

Any

Many rules can match but matched rules must have same output

P

Priority

Many rules can match and matched rules can have different outputs; output selected per a prioritised list of possible outputs

F

First

Many rules can match and matched rules can have different outputs; output selected per ordering of rules

O

Output

Matched rule outputs are returned in order per a prioritised list of possible outputs

R

Rule

Matched rule outputs are returned in order per ordering of rules

C

Collect

No operator

Matched rule outputs are returned in arbitrary order

Collect operator (+, , #)

Operator (sum, min, max, count) applied to the outputs and the result returned

C+ C> C< C#

= DEFAULT POLICY

DMN Spec Example

DRD

BKM(s)

THANK YOU • Credits: • OMG DMN standards team standardising notations for best practice decision analysis and design • Larry Goldberg and Barbara Vonhalle defining The Decision Model as a best practice methodology • Sapiens DECISION product team permitting the use of their tool for this presentation