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Requirements-Based Testing for Model Development

Test an autopilot subsystem against a requirement.

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';
reqDoc = 'RollAutopilotRequirements.txt';

Open the Test File and Model

Open the RollAutopilotMdlRef model. The full control system TestAndVerificationAutopilotExample references this model.

open_system(fullfile(filePath,rollModel));

Open the test file in the Test Manager.

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

You can also open the test file by clicking Apps > Simulink Test (under Model Verification, Validation, and Test). Then, click Simulink Test Manager and open the test file in the filePath location.

Open the requirements document. In the test browser, expand AutopilotTestFile and Basic Design Test Cases in the tree, and click Requirement 1.3 test. In the Requirement 1.3 test tab, expand Requirements. Double-click on any of the requirements links to open the Requirements Editor, where you can review the requirements.

In the document, requirement 1.3.1 states: When roll hold mode becomes the active mode, the roll hold reference shall be set to the actual roll angle of the aircraft, except under the conditions described in the child requirements.

  • Child requirement 1.3.1.1 states: The roll hold reference shall be set to zero if the actual roll angle is less than 6 degrees, in either direction, at the time of roll hold engagement.

  • Child requirement 1.3.1.2 states: The roll hold reference shall be set to 30 degrees in the same direction as the actual roll angle if the actual roll angle is greater than 30 degrees at the time of roll hold engagement.

  • Child requirement 1.3.1.3 states: The roll reference shall be set to the cockpit turn knob command, up to a 30 degree limit, if the turn knob is commanding 3 degrees or more in either direction.

The test case creates three scenarios to test the normal conditions and exceptions in the requirement.

The requirements document traces to the test harness using URLs that map to the Test Sequence block and test steps. Open the test harness and highlight the component associated with reference requirement 1.3.

sltest.harness.open([rollModel '/Roll Reference'],testHarness)
rmi('highlightModel','RollReference_Requirement1_3')

The Test Sequence block, Test Assessment block, and component under test link to the requirements document. Highlight requirements links by selecting Apps > Requirements Manager and then, clicking Highlight Links in the test harness model. You can also highlight links in the Test Sequence Editor by clicking Toggle requirements links highlighting in the toolstrip.

Test Sequence

Open the Test Sequence block.

open_system('RollReference_Requirement1_3/Test Sequence')

The Test Sequence block creates test inputs for three scenarios:

In each test, 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.

These scenarios check basic component function, but do not necessarily achieve objectives such as 100% coverage.

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 covering:

  • 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.

Verify the Subsystem

To run the test, in the Test Manager, right-click Requirement 1.3 Test in the Test Browser pane, and 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. Click Subplots in the toolstrip 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. Close the test harness.

  2. Add a Saturation block to the model as shown.

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

  4. 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.

close_system(rollModel,0);
close_system(topModel,0);
close_system('RollRefAssessLib',0);
sltest.testmanager.clear;
sltest.testmanager.clearResults;
sltest.testmanager.close;
clear filePath topModel reqDoc rollModel testHarness testFile harnessLink