1. Testing (Continued)

2. Test-Driven Development
The tests are the detailed specification
And now can be executed, not just read
More tests
Fewer specification documents

3. Types of Tests System: End-to-end tests
User-like input to end-user output
End to End Tests
Unit Tests
Test small pieces of system (single classes / functions)
Unit Tests

4. System Tests vs. Unit Tests
Strengths/Weaknesses of System Tests
Strengths/Weaknesses of Unit Tests

5. System Tests vs. Unit Tests
Strengths/Weaknesses of System Tests
Test entire system  no gaps
Hard to debug: problem could be anywhere!
Fragile: often test exact user input would produce exact output text / file
Strengths/Weaknesses of Unit Tests
Easier to debug: start with 1 class / function
Less fragile: Don’t check user interface (I/O): check API / class does what it should with code (testfixture)
Don’t test whole system  gaps possible

6. Types of Tests Fewer Integration Tests Bigger unit tests
(but not 0!)
End to End Tests
Integration Tests
Bigger unit tests
But now test multiple classes / bigger functionality
Moderate difficulty to debug
Integration Tests
Unit Tests
More

7. Unit Tests Want: No! To test individual classes / functions How?
Carefully chosen user input?
Output ...
No!
struct Point {
float x;
float y;
t_point& operator*=(float rhs);
. . .

8. 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

9. Unit Tests myCode.cpp struct Point { float x; float y;
t_point& operator*=(float rhs);
. . .
tester.cpp
int test1 () {
Point testme (1, 2);
testme *= 3;
if (testme != Point (3, 6)) {
cout << “uh – oh” << endl;
return (1); }
return (0);
test_main.cpp
g++ myCode.cpp main.cpp –o prog.exe
int main () {
int error = 0;
error += test1();
. . . // Lots more tests
g++ myCode.cpp tester.cpp
test_main.cpp –o test.exe

10. 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

11. “Test the Seams” Overlapping tests good Therac-25
Your code + partner’s code
Both unit tested
Make sure there’s an integration test
Therac-25

12. Testing Tools What tools? Debugger Memory checker
Use to debug when a test fails
Use to verify new code
Step through it and watch execution
Memory checker
Program seg faults?
Program behaving very strangely?
Maybe you are accessing memory you shouldn’t be!
Run debug_check configuration and/or valgrind

13. Testing Tools 3. Code coverage
Tools that can track what lines of your programs have executed over all your tests
MyCode.cpp
int someFunc (int input) {
if (input == 0)
return (3);
else
return (7); }
main.cpp
int main () {
int j = someFunc (8);
// Wow I’m bad at testing! }

14. Testing Tools 3. Code coverage
Tools that can track what lines of your programs have executed over all your tests
MyCode.cpp
int someFunc (int input) {
if (input == 0)
return (3);
else
return (7); }
No test reaches this line.
Code coverage: 6 out of 7 lines or 86%
main.cpp
int main () {
int j = someFunc (8);
// Wow I’m bad at testing! }

15. Google: Testing so Important, Tutorials in the Bathroom

16. “Testing on the Toilet”

17. Automate Build & Tests Make it easy to do the right thing Ece297:
One command to build
One command to test
One command to submit
Google
Also easy to build, test
Easy to deploy
Send to the real web site and real users
Split into A/B test (e.g. 2% of web traffic gets new ad engine)
Easy to reverse deployment if a bad idea
Continuous deployment: requires good automated tests

18. Good Coding Style

19. 1. Use White Space White space: show code organization
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) {
White space: show code organization
Indent properly (3 or 4 spaces) per { }.
Leave blank lines between functions / key blocks

20. float di (float a, float b) { float val, d, x, x2, y; d = 1
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?

21. 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?

22. 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;

23. 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?

24. Comment what whole function does
// 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

25. Comments: Usefulness? asteroids.cpp
/* This file implements an asteroid AI. It maintains
* a current position and velocity for each asteroid and
* the ship. It divides the screen into N bins, and
* computes the desirability of moving the ship
* to each bin by computing the time at which the ship
* could it, and the bin’s asteroid density at that time. */
StudentRecord.h
/* Main data structure used to store all information
* about a U of T student. Linked list. */
struct StudentRecord {
int nClassesCurrent; // Number enrolled, current semester
int nClassesComplete; // Number completed & passed
StudentRecord *next; // Pointer to next (linked list) record
program.cpp
// Compute the sum of the array, over all its elements
int sum = 0;
for (int i = 0; i < nElem; i++)
sum += array[i];

26. 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
Top of files
// Functions to simulate resistor network. Proceeds in 6 stages …
Class / data structure definitions
Understand the data  can understand the program!
Start of functions
Tricky code
Not useful:
Comments that translate C++ to English
Most important
Least important

27. Thoughts on This Code? Using a “magic number”: 20
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);
Using a “magic number”: 20
Change array size: must find and change all 20’s
Returning magic numbers: -1, 0, 1
Must read code carefully to see what each means

28. 4. Use Named Constants
const int NUM_WEIGHTS = 20; // 1. Constant variable
#define WEIGHT_ZERO // 2. Pre-processor constant
enum 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)

29. 5. Many Short Functions Short functions Easier to re-use
Fix bugs in one place, not many
Make code easier to read: more abstraction
How long should functions be?
Should have many 5 to 10 line functions
Should very rarely have a function > 100 lines

30. There is no honour in copy
Thoughts on This Code?
#include <math.h>
void myFunc (float a[], float b[], int nvals) {
float absAvg1 = 0;
for (int i = 0; i < nvals; i++)
absAvg1 += abs(a[i]);
absAvg1 /= nvals;
float absAvg2 = 0;
absAvg2 += abs(b[i]);
absAvg2 /= nvals;
... }
There is no honour in copy
and paste coding!
Refactor!

31. Better Version? 1. Not much shorter, but easier to read
#include <math.h>
float compAbsAvg (float array[], int nvals) {
float absAvg = 0;
for (int i = 0; i < nvals; i++)
absAvg += abs (array[i]);
return (absAvg / nvals); }
void myFunc (float a[], float b[], int nvals) {
float absAvg1 = compAbsAvg (a, nvals);
float absAvg2 = compAbsAvg (b, nvals);
...
1. Not much shorter, but easier to read
2. Less chance of more code copying  future code will be shorter

32. 6. Don’t Do Too Much in a Statement / Line
#include <string>
#include “StreetsDatabaseAPI.h”
string name = getIntersectionName(getStreetSegmentInfo( getIntersectionStreetSegment(0,startInter)).to);
// Hard to read!
unsigned firstSeg = getIntersectionStreetSegment (0,startInter);
unsigned destInterId = getStreetSegmentInfo(firstSeg).to;
string destInterName = getIntersectionName (destInterId);
// Show your work  divide into several steps on several lines
// Use good variable names to show what intermediate results
// are.

33. 7. Group Related Data into Classes
vector<int> fromIntersectionofSegment; vector<int> toIntersectionofSegment; vector<float> speedLimitofSegment; vector<double> lengthofSegment;
class SegmentData {
public:
int fromIntersectionIdx;
int toIntersectionIdx;
bool oneWay; // If true, can only go from -> to
float speedLimit; // In km/h
double travelTime (); // Returns travelTime in s }
vector<SegmentData> segmentInfo; // [0..numStreetSeg-1]
1. Groups related data and functions
2. Less name pollution

34. 8. Defensive Coding Use assertions to verify assumptions in your code
void myFunc (int *ptr) {
// Don’t ever call myFunc with a NULL ptr!
if (*ptr == 1) { …
#include <assert.h>
assert (ptr != NULL);
Exits program if ptr is NULL (condition not true)
Better than a comment:
Checked at runtime & gives useful error message
> assert failed on line 208 of file myFunc.cpp: ptr != NULL

35. What If I Need That Last Bit of Speed?
#define NDEBUG // Just turned off assertion checking
// Make sure this line is in front of
// #include <assert.h>
#include <assert.h>
void myFunc (int *ptr) {
ptr = NULL;
assert (ptr != NULL); // Not checked  won’t fire. …
Can turn off assertion checking in release build
Avoids any speed overhead
Leave on for debug build for extra checking
And maybe leave on in release too if your program not very time critical

36. 8. Defensive Coding B. Set deleted / invalid pointers to NULL
delete (ptr);
ptr = NULL; // Now we’ll crash if we try to use it  good! …
ptr->value = 1; // Will seg fault immediately
C. Self-checking code (advanced technique)
program_ok = validate_key_data_structure (my_struct);

37. Should have used assert or validity checkers!

38. Find the Bug!
const int NUM_WEIGHTS = 20; // 1. Constant variable #define WEIGHT_ZERO 0 // 2. Pre-processor constant enum 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_ZERO); if (weights[i] < 0) return (HAS_NEG); } return (ALL_POS);
Test program, find a failing case …
weights = {-1, 2, 3, 4, 5, 6, … 20}
checkWeights returns ALL_POS

39. 9. Use Compiler Warnings
> g++ -Wall weights.cpp > weights.cpp: In function ‘int checkWeights(int*)’: > weights.cpp:11: warning: suggest parentheses around assignment used as truth value
int checkWeights (int weights[NUM_WEIGHTS]) { for (int i = 0; i < NUM_WEIGHTS; i++) {
if (weights[i] = 0)
return (HAS_ZERO);
if (weights[i] < 0)
return (HAS_NEG); }
return (ALL_POS);
Line 11

40. Warnings in your code  lower style mark
9. No Warnings
Don’t have any warnings in your code
Warnings flag potentially problematic code
If you leave some warnings in, hard to see new ones
Fix right away: stay at 0 warnings!
Tell compiler to generate all useful warnings (more than default)
Command line: g++ –Wall <…>
We turn on all warnings we consider useful in your makefile
Warnings in your code  lower style mark

41. Summary: One Code Base to Rule Them All
Code will be read more than written
By you
By others
Make it readable!
Code will be modified many times
Make small functions & avoid repeated code
Keep the tests with the code
Automated, so you can re-run often
Keep documentation in the code -- comments!

42. Read code as a team & share feedback
Code Reviews
If you do one thing for code quality  code reviews
Altera/Intel: periodic review
4 reviewers read code written by one team member
Significant amount: ~400 – 1000 lines
Write down thoughts
Then meet to discuss  readable, clear, efficient?
Google: every commit reviewed and approved
Integrated into source code control system
Change not visible to others until reviewed & approved
Read code as a team & share feedback