What is a branch in code coverage for javascript unit testing -

i use istanbul code coverage of unit tests in angularjs project. there 4 types of coverage , statement, branch, function , line coverage. statement, function , line allright don't understand "branch" is. explain branch is? thanks

a branch runtime can choose whether can take 1 path or another. lets take following example:

if(a) {     foo(); }  if(b) {     bar(); }  yay(); 

when reaching first line, can decide if wants go inside body of if(a)-statement. also, can decide not that. @ stage, we've seen 2 paths (one branch).

the next statement after gets more interesting. can go inside if body , execute bar. can not that. remember we've had branch before. result may vary if foo called or not.

so end 4 possible paths:

• not calling foo, not calling bar either
• calling foo, not calling bar
• not calling foo, calling bar
• calling both foo , bar

the last yay executed, no matter if foo or bar called, doesn't count branch. code snippet above contains 4 paths / 2 branches.

like other answers have mentioned, there numerous statements can cause branch (if/switch). don't forget conditional-loops, such while/for/do-while though.

the code coverage tool wants make sure you've tested branches. best if paths have been tested, not branches. this, make sure no unwanted behavior executed.