**Simple path**

A simple path is a path in which any node can’t appear more than once but only starting and ending nodes can appear more than once.

**Prime Path**

The prime path is basically *a simple path and it does not appear as a subpath of any other simple path.*

**Simple Paths**

In the figure, followings are the simple paths.

**Length 0:**

Following nodes represents simple paths with length 0 because having no outgoing edge.

Simple paths = [0], [1], [2], [3]

**Length 1:**

Following nodes represents simple paths with length 1 because having total 1 outgoing edge.

Simple paths = [ 0, 1], [ 0, 2 ], [ 1, 3 ], [ 2, 3 ], [ 3, 0 ],

**Length 2:**

Following nodes represents simple paths with length 2 because having total 2 outgoing edges.

Simple paths = [ 0, 1, 3 ], [ 0, 2, 3 ], [ 1, 3, 0 ], [ 2, 3, 0 ],[ 3, 0, 1 ], [3, 0, 2 ],

**Length 3:**

Following nodes represents simple paths with length 3 because having total 3 outgoing edges.

Simple paths = [ 0, 1, 3, 0 ], [ 0, 2, 3, 0], [ 1, 3, 0, 1 ], [ 2, 3, 0, 2 ], [ 3, 0, 1, 3 ], [ 3, 0, 2, 3 ], [ 1, 3, 0, 2 ],[ 2, 3, 0, 1 ].

**Prime Paths :**

All of the following simple paths are the prime path.

[ 0, 2, 3, 0], [ 0, 1, 3, 0 ], [ 2, 3, 0, 2 ], [ 1, 3, 0, 1 ], [ 3, 0, 2, 3 ], [ 3, 0, 1, 3 ], [ 2, 3, 0, 1 ] , [ 1, 3, 0, 2 ]

__Round-Trip Path__

*A *Round-Trip Path is a path *that starts and ends with the same nodes.*

**Prime path coverage criteria(PPC)**

*According to prime path coverage(PPC), each prime path must be covered in test requirements.*

*Some facts about PPC:*

*PPC*subsumes node coverage.*PPC*subsumes edge coverage.