Creating a model using yEd

This describes the syntax for GraphWalker and the rules for creating a model using the yEd model editor.

The model is a directed graph

The objective of the model is to express the expected behavior of the system under test. To do so, we use a directed graph, in which a vertex (or a node) represents some desired state, and the edges (arcs, arrows, transitions) represents whatever actions we need to do in order to achieve that desired state.

For example, let us take a web site that requires authentication before we can access the site's content. Designing a test, using a directed graph, might look like this:

Vertex

A vertex represents an expected state that we want to examine. In any implementing code/test, this is where you will find the assertions, or the oracles.

• In yEd a vertex is called a node, normally depicted as a box.
• GraphWalker does not care what color or shape a vertex has.

Edge

An edge represents the transition from one vertex to another. It is whatever action is needed to be made in order to reach the next state. It could be selecting some menu choice, clicking a button, or making a REST API call.

• GraphWalker only accepts one-way directed edges (arrows).
• GraphWalker does not care what color or thickness an edge has.

The Rules

This section will talk about the modeling rules using yEd with GraphWalker.

Start vertex

• The Start vertex is not mandatory.
• If used, there must be 1 (and only 1) vertex with the name Start in the model.
• There can only be 1 out-edge from the Start vertex.
• The Start vertex will not be included in any generated path.

Name of a vertex or edge

The name is the first word, on the first line, in a label for an edge or vertex.

Label

Labels are all the text associated with an edge or a vertex.

Vertex and edge names

Guards - Only for an edge

Guards are mechanisms only associated with edges. Their role is the same as an if-statement, and makes an edge eligible or not for being walked. The guard is a conditional expression enclosed between square brackets:

[loggedIn == true]

This means that if the attribute loggedIn equals true, the edge is eligible.

Action - Only for an edge

Action is a mechanism only associated to edges. This is javascript code that we want to execute in the model. It is placed after a forward slash. Each statement must end with a semicolon.

/loggedIn=false; rememberMe=true;

The purpose of the action code is to serve as data to the guards.

Example

This example illustrates how actions and guards work.

1. Let us start with the out-edge from the Start vertex:

e_Init/validLogin=false;rememberMe=false;

The name of the edge is e_Init, followed by a forward slash, denoting that text from that point until end-of-line is action code. The action initializes 2 attributes: validLogin and rememberMe.

2. When we have walked the edge above, we arrive at the v_ClientNotRunning vertex. This vertex has 2 out-edges, which both have guards. Since both validLogin and rememberMe are at this point initialized to false, only 1 edge is accessible for walking: the edge e_Start that has the vertex v_LoginPrompted as destination.

3. Now let us say that we have traversed the edges e_ToggleRememberMe and e_ValidPremiumCredentials, and arrive again at the vertex v_ClientNotRunning. We would now expect GraphWalker to select the other edge e_Start that has the vertex v_Browse as destination.

This illustrates how we can direct and control flows through a graph, if needed.

Global attributes - Share data between models

In the examples above, where loggedIn, validLogin and rememberMe were used as attributes to hold data in the model, they cannot be shared between models.

To achive that, a global attribute is used instead. Like this:

For an action:

/global.loggedIn=false; global.rememberMe=true;

For a guard:

[global.loggedIn == true]

Keywords

Keywords are used in the model to increase functionality and usability.

• Start - This is used in a vertex to denote the Start vertex. Only one Start vertex per model.

• BLOCKED - A vertex or an edge containing this keyword will be excluded when a path is generated. If it is an edge, it will simply be removed from the graph. If it is a vertex, the vertex will be removed with its in- and out-edges.

• SHARED - This keyword is only for vertices. It means that GraphWalker can jump out of the current model to any other model, to a vertex with the same SHARED name.
  The syntax is:
  

SHARED:SOME_NAME

• INIT - This keyword is only for vertices. When using data in a model, this data needs to be initialized which is what this keyword does. INIT is allowed in more vertices than just one.
  The syntax is:
  

INIT:loggedIn=false; rememberMe=true;

• REQTAG - This keyword is only for vertices. A comma-separated list of requirements used to create traceability with external requirements and the models.
  The syntax is:
  

REQTAG:String1, String2

• weight - This keyword is only for edges. Can only be used with the weighted random generator. It holds a real value between 0 and 1, and represents the probability that the edge is chosen. For example, a value of 0.05 means a 5% chance of that edge being selected. The image below has 2 out-edges from vertex v_LoginPrompted that uses the keyword weight.
  The syntax is:
  

weight=*float value between 0.0 and 1.0*

Multiple models

GraphWalker can work with several models in one session. It means that when generating a path, GraphWalker can choose to jump out of one model into another one. This is very useful when separating different functionality into different models. For example, if you have a system that you want to test and you would need to log in to do that, then it might make sense to create a single model handling the login functionality, and other models to handle whatever else you want to test. The login model could then be reused for every other test scenario.

It is not the same thing as flattening

When flattening models, several models are merged into one single model, which is then traversed. This is not the case here. GraphWalker is executing every model in its own context. The scope of the data in the models are not shared between them.

SHARED:SOME_NAME

The mechanism that controls the jumping between the models is the keyword SHARED. Let us look at an example. Consider these 4 models:

All models are loaded into GraphWalker, and the first model (Model A) is where the path generation is started. Using graphwalker-cli, the command could look something like this:

java - jar graphwalker-cli-4.3.1.jar offline -m src/test/resources/graphml/shared_state/Model_A.graphml "random(edge_coverage(100))" \
 -m src/test/resources/graphml/shared_state/Model_B.graphml "random(edge_coverage(100))" \
 -m src/test/resources/graphml/shared_state/Model_C.graphml "random(edge_coverage(100))" \
 -m src/test/resources/graphml/shared_state/Model_D.graphml "random(edge_coverage(100))"

When the path generation reaches the vertex v_B in Model A, it has to consider the keyword SHARED:B. This tells GraphWalker to search all other models for the same keyword using the same name: B. In our case, there is only one, and it is in Model B. GraphWalker makes a decision whether to jump out of Model A to the vertex v_B in Model B, or to stay in Model A. This decision is random.

Also, if the path generation is executing in Model B, and it reaches the vertex v_B, GraphWalker can jump out of Model B, back to vertex v_B in Model A.