## Transitions, Temporal Operators, and Messages in Test Sequence Blocks

### Transition Between Steps Using Temporal or Signal Conditions

The Test Sequence block uses MATLAB® as the action language. You can transition between test steps by evaluating the component under test. You can use conditional logic, temporal operators, and event operators.

Consider a simple test sequence that outputs a sine wave at three frequencies. The Test Sequence block steps through several actions based on changes in the signal switch. See hasChanged.

### Temporal Operators

To create an expression that evaluates the simulation time, use temporal operators. Variables used in signal conditions must be inputs, parameters, or constants in the Test Sequence block.

OperatorSyntaxDescriptionExample
et

`et(TimeUnits)`

The elapsed time of the test step in `TimeUnits`. Omitting `TimeUnits` returns the value in seconds.

The elapsed time of the test sequence step in milliseconds:

`et(msec)`
t

`t(TimeUnits)`

The elapsed time of the simulation in `TimeUnits`. Omitting `TimeUnits` returns the value in seconds.

The elapsed time of the simulation in microseconds:

`t(usec)`
after

`after(n, TimeUnits)`

Returns `true` if `n` specified units of time in `TimeUnits` elapse since the beginning of the current test step.

After 4 seconds:

`after(4,sec)`
before

`before(n, TimeUnits)`

Returns `true` until `n` specified units of time in `TimeUnits` elapse, beginning with the current test step.

Before 4 seconds:

`before(4,sec)`
duration

`ElapsedTime = duration (Condition, TimeUnits)`

Returns `ElapsedTime` in `TimeUnits` for which `Condition` has been `true`. `ElapsedTime` is reset when the test step is re-entered or when `Condition` is no longer `true`.

Return `true` if the time in milliseconds since `Phi > 1` is greater than 550:

`duration(Phi>1,msec) > 550`

Syntax in the table uses these arguments:

### Transition Operators

To create expressions that evaluate signal events, use transition operators. Common transition operators include:

OperatorSyntaxDescriptionExample
hasChanged
```hasChanged(u) ```

Returns `true` if `u` changes in value since the beginning of the test step, otherwise returns `false`.

`u` must be an input data symbol.

Transition when `h` changes:

`hasChanged(h)`
hasChangedFrom
```hasChangedFrom(u,A) ```

Returns true if `u` changes from the value `A`, otherwise returns false.

`u` must be an input data symbol.

Transition when `h` changes from `1`:

`hasChangedFrom(h,1)`
hasChangedTo
```hasChangedTo(u,B) ```

Returns true if `u` changes to the value `B`, otherwise returns false.

`u` must be an input data symbol.

Transition when `h` changes to `0`:

`hasChangedTo(h,0)`

### Use Messages in Test Sequences

Messages carry data between Test Sequence blocks and other blocks such as Stateflow® charts. Messages can be used to model asynchronous events. A message is queued until you evaluate it, which removes it from the queue. You can use messages and message data inside a test sequence. The message remains valid until you forward it, or the time step ends. For more information, see Messages (Stateflow) in the Stateflow® documentation.

Receive Messages and Access Message Data

If your Test Sequence block has a message input, you can use queued messages in test sequence actions or transitions. Use the `receive` command before accessing message data or forwarding a message.

To create a message input, hover over Input in the Symbols sidebar, click the add message icon, and enter the message name.

`receive(M)` determines whether a message is present in the input queue `M`, and removes the message from the queue. `receive(M)` returns `true` if a message is in the queue, and `false` if not. Once the message is received, you can access the message data using the dot notation, `M.data`, or forward the message. The message is valid until it is forwarded or the current time step ends.

The order of message removal depends on the queue type. Set the queue type using the message properties dialog box. In the Symbols sidebar, click the edit icon next to the message input, and select the Queue type.

Send Messages

To send a message, create a message output and use the `send` command. To create a message output, hover over Output in the Symbols sidebar, click the add message icon, and enter the message name.

You can assign data to the message using the dot notation `M.data`, where M is the message output of the Test Sequence block. `send(M)` sends the message.

Forward Messages

You can forward a message from an input message queue to an output port. To forward a message:

1. Receive the message from the input queue using `receive`.

2. Forward the message using the command `forward(M,M_out)` where `M` is the message input queue and `M_out` is the message output.

Compare Test Sequences Using Data and Messages

This example demonstrates message inputs and outputs, sending, and receiving a message. The model compares two pairs of test sequences. Each pair is comprised of a sending and receiving test sequence block. The first pair sends and receives data, and the second sends and receives a message.

Set the model name variable.

```model = 'sltest_testsequence_data_vs_message'; ```

Open the model.

```open_system(model) ```

Test Sequences Using Data

The DataSender block assigns a value to a data output `M`.

The DataReceiver block waits 3 seconds, then transitions to step S2. Step S2 transitions to step S3 using a condition comparing `M` to the expected value, and does the same for S3 to S4.

Test Sequences Using Messages

The MessageSender block assigns a value to the message data of a message output `M_out`, then sends the message to the MessageReceiver block.

The MessageReceiver block waits 3 seconds, then transitions to step S2. Step S2's transition evaluates the queue `M` with `receive(M)`, removing the message from the queue. `receive(M)` returns `true` since the message is present. `M.data == 3.5` compares the message data to the expected value. The statement is true, and the sequence transitions to step S3.

When step S3's transition condition evaluates, no messages are present in the queue. Therefore, S3 does not transition to S4.

Run the test and observe the output comparing the different behaviors of the test sequence pairs.

```open_system([model '/Scope']) sim(model) ```

```close_system(model,0) clear(model) ```