Agile Development & Companies • Harvard Business Review: “Why the lean start-up changes everything ” • Agile development applied to entire business of start-ups Itera te! Simplest possible prototype! Image: leadnet.org
Agile Development & Companies
• Harvard Business Review: “Why the lean start-up changes everything”
• Agile development applied to entire business of start-ups
Iterate!
Simplest possible
prototype!
Image: leadnet.org
Testing Philosophy
• “If you didn’t test it, it doesn’t work”– Assume all code broken until proven otherwise– Look at what the program does not what it is
supposed to do• Scientist: you are testing hypotheses about program
– Think of every case your program should handle cover them all
Testing Time
• Develop tests as or before you code– Test-driven development
Test & Evaluate
Refine
Prototype
Test-Driven Development
• The tests are the detailed specification– And now can be executed, not just read
Less specification document
More tests
Types of Tests
Unit Tests
End to End Tests
End-to-end (system) tests• Test entire system (like end user would)• Hard to debug a failure problem could be anywhere!• Fragile: often test some exact user input would
produce some exact output text / file
Unit Tests• Test small pieces of system (single classes / functions)• Much easier to debug a failure start with that class /
function• Don’t check user interface (I/O): check API / class
does what it should with code (testfixture)
Types of Tests
Unit Tests
Integration Tests
End to End Tests
Integration Tests• Bigger unit tests• Work the same way• But now test multiple classes / bigger functionality• Moderate difficulty to debug
Testing Automation
• You will re-test often– Every time you change the program– How to speed up?
• System tests: save in files– Use file redirection
• prog.exe < in.txt > out.txt • diff out.txt out_good.txt // matched known good result?
– Less fragile• Write validity checker instead of checking exact output match
• Write scripts to run all tests and check results
Unit Tests
• Want:– To test individual classes / functions– How?
• Carefully chosen user input?
struct Point { float x; float y; t_point& operator*=(float rhs); . . .
Output ...
No!
Unit Tests
• Write new code – To put class in right state– To directly send it some input / make some calls– To immediately check the responses– Test driver
Unit Tests
struct Point { float x; float y; t_point& operator*=(float rhs); . . .
int test1 () { Point testme (1, 2); testme *= 3; if (testme != Point (3, 6)) { cout << “uh – oh” << endl; return (1); } return (0);}
myCode.cpp
tester.cpp
int main () { int error = 0; error += test1(); . . . // Lots more tests
test_main.cpp
g++ myCode.cpp tester.cpp test_main.cpp –o test.exe
g++ myCode.cpp main.cpp –o prog.exe
Unit Test Frameworks• Lots of repetitive code to create test drivers
– Set up the test– Check if the test passed– Run all the tests– Output appropriate messages– Collect statistics
• Unit Test Frameworks– Useful macros (#defines) and functions to simplify
coding– We are using UnitTest++
• Powerful, but easy to learn• ECE 297 Unit Test Quick Start Guide
TEST(..) or TESTFIXTURE (…)
CHECK(..)
RunAllTests()
Automatic
Automatic
“Test the Seams”
• Overlapping tests good– Your code + partner’s code
• Both unit tested
– Make sure there’s an integration test
• Therac-25
Testing Tools
• What tools?
1.Debugger– Use to debug when a test fails– Use to verify new code
• Step through it and watch execution
2.Memory checker– Program seg faults?– Program behaving very strangely?– Maybe you are accessing memory you shouldn’t be!– Run valgrind
Testing Tools
3. Code coverage– Tools that can track what lines of your programs have
executed over all your tests
int someFunc (int input) { if (input == 0) return (3); else return (7);}
MyCode.cpp
int main () { int j = someFunc (8); // Wow I’m bad at testing!}
main.cpp
Testing Tools
3. Code coverage– Tools that can track what lines of your programs have
executed over all your tests
int someFunc (int input) { if (input == 0) return (3); else return (7);}
MyCode.cpp
int main () { int j = someFunc (8); // Wow I’m bad at testing!}
main.cpp
No test reaches this line.Code coverage: 6 out of 7 lines or 86%
1. Use White Space
White space: show code organization– Indent properly (3 or 4 spaces) per { }.– Leave blank lines between functions / key blocks
int sumVec (int vec[], int nElem) {int i, result = 0;for (i = 0; i < nElem; i++) {result += vec[i];}return (result);}void nextFunc (int i) {…
int sumVec (int vec[], int nElem) { int i, result = 0; for (i = 0; i < nElem; i++) { result += vec[i]; } return (result);}
void nextFunc (int i) {
float di (float a, float b)
{
float val, d, x, x2, y;
d = 1.e-4;
val = 0;
for (x = a; x < b; x += d) {
x2 = x + d;
if (x2 > b)
x2 = b;
y = 0.5 * ((1. / x) + (1. / x2));
val += y * (x2 - x);
}
return (val);
}
What does this do?
float definite_integral (float x_left, float x_right)
{
float integral, step_size, x1, x2, y_average;
step_size = 1.e-4;
integral = 0;
for (x1 = x_left; x1 < x_right; x1 += step_size) {
x2 = x1 + step_size;
if (x2 > x_right)
x2 = x_right;
y_average = 0.5 * ((1. / x1) + (1. / x2));
integral += y_average * (x2 – x1);
}
return (integral);
}
What does this do?
2. Descriptive Variable Names
• Use descriptive names– Variables, functions, structs/types, …
• get_file_name ( ); // Use _ to separate• getFileName (); // Or use upper case to mark words
• Types: start with a capital letter• Variables: start with lowercase
– class MyClass { …– MyClass oneVar;
float definite_integral (float x_left, float x_right)
{
float integral, step_size, x1, x2, y_average;
step_size = 1.e-4;
integral = 0;
for (x1 = x_left; x1 < x_right; x1 += step_size) {
x2 = x1 + step_size;
if (x2 > x_right)
x2 = x_right;
y_average = 0.5 * ((1. / x1) + (1. / x2));
integral += y_average * (x2 – x1);
}
return (integral);
}
What does this do?
// Compute the definite integral of 1/x between x_left and x_right via the
// trapezoidal method. Smaller values of step_size improve accuracy, but
// increase computation time.
float definite_integral_of_one_over_x (float x_left, float x_right)
{
float integral, step_size, x1, x2, y_average;
step_size = 1e-4;
integral = 0.;
for (x1 = x_left; x1 < x_right; x1 += step_size) {
x2 = x1 + step_size;
if (x2 > x_right) // in case (x_right – x_left) is not a multiple of step_size
x2 = x_right;
y_average = 0.5 * ((1. / x1) + (1. / x2)); // average of y(x1) and y(x2)
integral += y_average * (x2 – x1);
}
return (integral);
}
Comment what whole function does
Comment any tricky bits of code
Comments: Usefulness?/* Functions to simulate transistors. * We model transistors as nonlinear elements, * by looking up the source-drain current for each V … */
trans_sim.cpp
/* Main data structure used to store all information * about a U of T student. Linked list. */struct StudentRecord { int nClassesCurrent; // Number of classes enrolled in. int nClassesComplete; // Number of completed classes, // not including currently enrolled ones StudentRecord *next; // Pointer to next (linked list) record
StudentRecord.h
// Compute the sum of the array, over all its elementsint sum = 0;for (int i = 0; i < nElem; i++) sum += array[i];
program.cpp
3. “High-Level” Comments• Most important comments: give the big picture
– Documentation should be in the comments– Not a separate document will get out of date
1. Top of files // Functions to simulate transistors. We proceed in 6 stages …
2. Class / data structure definitions– Understand the data can understand the program!
3. Start of functions
4. Tricky code
Not very useful comments:– Translate C++ to English
Most important
Leastimportant
Thoughts on This Code?int checkWeights (int weights[20]) { for (int i = 0; i < 20; i++) { if (weights[i] < 0) return (-1); if (weights[i] == 0) return (0); } return (1);}
1. Using a “magic number”: 20– Change array size: must find and change all 20’s
2. Returning magic numbers: -1, 0, 1– Must read code carefully to see what each means
4. Use Named Constantsconst int NUM_WEIGHTS = 20; // 1. Constant variable#define WEIGHT_ZERO 0 // 2. Pre-processor constantenum WtReturn {HAS_NEG = -1, HAS_ZERO = 0, ALL_POS = 1}; // 3. make an “enumeration” (list) of int constants
int checkWeights (int weights[NUM_WEIGHTS]) { for (int i = 0; i < NUM_WEIGHTS; i++) { if (weights[i] < 0) return (HAS_NEG); if (weights[i] == 0) return (HAS_ZERO); } return (ALL_POS);}• Three ways to make constants use any way you like• Name: ALL CAPITALS (convention)