Lab2.md

Lab

Review slides on Coverage

You may work with a partner.

Use the chance to better understand statement and branch coverage. You will certainly be tested on this material. Practice now.

Statement Coverage

Exercise

What is the statement coverage below

public void Simple(int i)
{
   if( i < 0 )
      return;
}

How many statements are there?

Answer: It depends. Coverage is typically done at a lower level than you see in your text editor. For example, there is actually an implicit return statement. You could say there are 3 statements. Object constructors can be counted, etc. In examinations, we will not be strict in what you consider a statement.

What is the statement coverage if you have a test suite of Simple(3)?

What is the statement coverage if you have a test suite of Simple(3), Simple(-3)?

Exercise

Given a list tweets with retweet count [ getRetweetCount(): 33 ], [getRetweetCount() : 3 ]? What is the statement coverage below?

public Status mostRetweeted(List<Status> list)
{
	int max = 0;
	Status maxStatus = list.get(0);
	for( Status s : list )
	{
		if( max < s.getRetweetCount() )
		{
			max = s.getRetweetCount();
			maxStatus = s;
		}
	}
	return maxStatus;
}

Hmm. Does for loops count? Yes. Coverage calculates the dynamic execution of the code. So every iteration of the loop should be evaluated. If just one case hits a statement, that's enough as far as coverage is concerned.

Branch Coverage

Branch coverage examines the number of branches (or decisions) taken during execution of a program.

Examine this example. You will be asked to extend it below.

Example

private static int maxValue(int[] chars) {

	if( chars.length == 0 )
	   return 0;

	int max = chars[0];
	for (int i = 0; i < chars.length; ktr++) {
		if (chars[i] > max) {
			max = chars[i];
		}
	}
	return max;
}

1. The program graph.

2. There are 3 decision nodes and 6 branches.

3. For a testsuite with the following test cases, how many branches are covered?

• maxminValue( [1,1,1,1] );
• maxminValue( [3,2] );

Answer: 4/6

Why?

• The true branch of the .length == 0 is never taken.
• The true branch of chars[i] > max is never taken.

Exercise

Someone decided to extend the method to calculate the min and max at the same time.

// Calculate the min and max value of an array of characters.
// min is stored in [0], max in [1].
private static int[] maxminValue(int[] chars) 
{
	if( chars.length == 0 )
		return null;
	
	int[] minmax = {chars[0], chars[0]};

	for (int i = 0; i < chars.length; i++)
	{
		if (chars[i] > minmax[1]) {
			minmax[1] = chars[i];
		}
		else if( chars[i] < minmax[0] )
		{
			minmax[0] = chars[i];
		}
	}

	return minmax;
}

1. Draw the program graph.
2. How many branches and decisions are there in total?
3. What the branch coverage __ / __ ?

The ability to answer this quesiton will seperate As from Bs on an exam.

Measuring Coverage.

You can use tools to help you measure coverage of your code and unit tests.

Install EclEmma.

http://eclemma.org/

Inspecting coverage

In your HW1.P2, run coverage on your code.

Notice an interesting mistake in the unit test. It will actually pass if there are no links with data-href found, because rank will still be zero!

The underlying problem is related to a difference in how google renders the search result pages for the Selenium driver and a real browser. Instead, another selector can be used to find the appropriate link:

List<WebElement> links = this.driver.findElements(By.xpath("//cite"));
for( WebElement link : links )
{
	if( link.getAttribute("data-href").equals("http://agile.csc.ncsu.edu/iTrust/wiki"))
		break;
	rank++;
}

Reports

You can view reports on coverage here:

HW1.P2

Spend time on completing your HW1.P2 assignment.