Requirements-Based Testing for Model Development

Test an autopilot subsystem against requirements.

This example demonstrates testing a subsystem against a requirement, using the test manager, test harness, Test Sequence block, and Test Assessment block. The requirements document links to the test case and test harness, and verify statements assess the component under test.

As you build your model, you can add test cases to verify the model against requirements. Subsequent users can run the same test cases, then add test cases to accomplish further verification goals such as achieving 100% coverage or verifying generated code.

This example tests the Roll Reference subsystem against a requirement using three scenarios. A Test Sequence block provides inputs, and a Test Assessment block evaluates the component. The Roll Reference subsystem is one component of an autopilot control system. Roll Reference controls the reference angle of the aircraft's roll control system. The subsystem fails one assessment, prompting a design change that limits the subsystem output at high input angles.

Paths and Example Files

Enter the following to store paths and file names for the example:

filePath = fullfile(matlabroot,'toolbox','simulinktest','simulinktestdemos');
topModel = 'TestAndVerificationAutopilotExample';
rollModel = 'RollAutopilotMdlRef';
testHarness = 'RollReference_Requirement1_3';
testFile = 'AutopilotTestFile.mldatx';

Open the Test File and Model

Open the test file in the Test Manager. You can also open the Test Manager by selecting Analysis > Test Manager from the Simulink menu.

tf = sltest.testmanager.load(fullfile(filePath,testFile));

Open the RollAutopilotMdlRef model.


View Test and Model Requirements

In the lower right corner of the canvas, click the icon and select the Requirements tile. The Requirements perspective shows requirements associated with the model. You can view model items or test cases that implement or verify a requirement by clicking the links.

In the test case, expand the Requirements section to view links to the requirement set.

Test Inputs

The test creates three scenarios to test normal conditions and exceptions in the Roll Hold Reference requirements. The test vectors are authored in the Test Sequence block.

Open the Test Sequence block.

sltest.harness.load([rollModel '/Roll Reference'],testHarness)
open_system('RollReference_Requirement1_3/Test Sequence')

For each scenario, the test sequence sets a signal level, then engages the autopilot. The test sequence checks that PhiRef is stable for a minimum time DurationLimit before it transitions to the next signal level. For the first two scenarios, the test sequence sets the EndTest local variable to 1, triggering the transition to the next scenario.

Test Assessments

Open the Test Assessment block.

open_system('RollReference_Requirement1_3/Test Assessment')

The Test Assessment block evaluates Roll Reference. The assessment block is a library linked subsystem, which facilitates test assessment reuse between multiple test harnesses. The block contains verify statements corresponding to:

  • The requirement that PhiRef = Phi when Phi operates inside the low and high limits.

  • The requirement that PhiRef = 0 when Phi < 6 degrees.

  • The requirement that PhiRef = 30 when Phi > 30 degrees.

  • The requirement that when TurnKnob is engaged, PhiRef = TurnKnob if TurnKnob >= 3 degrees.

Run the Test

In the Test Manager toolstrip, click Run.

The simulation returns verify statement results and simulation output in the Test Manager. The verify_high_pos statement fails.

  1. Click Results and Artifacts in the test manager.

  2. In the results tree, expand Verify Statements. Click Simulink: verify_high_pos. The trace shows when the statement fails.

  1. In the Data Inspector tab, click Subplots and select two plots arranged vertically. Select the lower plot in the Visualize pane.

  2. In the results tree, expand Results, Requirement 1.3 Test, and Sim Output.

  3. Select PhiRef and Phi. The output traces align with the verify results in the above plot. Observe that PhiRef exceeds 30 degrees when Phi exceeds 30 degrees.

Update RollReference to limit the PhiRef signal:

  1. Add a Saturation block as shown.

  2. Set the lower limit to -30 and the upper limit to 30.

  3. Link the block to its requirement. From the Requirements browser, drag requirement 1.1.2 to the Saturation block. An icon appears on the block, and the requirement is highlighted.

Run the test again. The verify statement passes, and the output in the test manager shows that PhiRef does not exceed 30 degrees.

clear filePath topModel reqDoc rollModel testHarness testFile