Getting Started with TESSY: Install, Import C Module, First Test Case, Coverage Report in 15 Minutes

Getting Started with TESSY: Your First Test Case and Coverage Report in 15 Minutes

The fastest way to evaluate a unit testing tool is to use it on your own code. This guide walks through the TESSY workflow from installation to first coverage report, using a simple C module as the example. By the end, you will have created a test case, executed it, and viewed the MC/DC coverage report.

Razorcat TESSY is available as an evaluation license through GSAS Micro Systems. Contact us at the end of this article to request one.

Step 1: Install TESSY

TESSY runs on Windows (the primary platform for embedded development in India). The installation is a standard Windows installer:

1. Run the TESSY installer
2. Activate the license (node-locked or floating, provided by GSAS)
3. Configure the compiler, point TESSY to your installed cross-compiler (Arm Compiler 6 via Keil MDK, IAR, TASKING, HighTec, or GCC)

The compiler configuration is the critical step. TESSY uses your project’s compiler to build test harnesses, so the test code compiles with the same toolchain as your production firmware. For teams in Bengaluru using Arm Keil MDK, point TESSY to the Arm Compiler 6 installation directory. For teams in Pune using TASKING for AURIX, point to the TASKING VX-toolset directory.

Step 2: Create a TESSY Project

Open TESSY and create a new project. The project stores all test configuration, test cases, and results. Specify:

• Project name: typically matching your firmware project name
• Compiler: the cross-compiler configured in Step 1
• Include paths: the header file directories from your firmware project
• Preprocessor defines: any project-level defines (e.g., TARGET_STM32F4, AUTOSAR_CLASSIC)

For this tutorial, we will use a simple temperature monitoring module:

// temp_monitor.h
##define TEMP_WARNING  80
##define TEMP_CRITICAL 100

typedef enum {
    TEMP_NORMAL,
    TEMP_WARNING_STATE,
    TEMP_CRITICAL_STATE
} TempStatus;

TempStatus evaluate_temperature(int current_temp, int rate_of_change);

// temp_monitor.c
##include "temp_monitor.h"

TempStatus evaluate_temperature(int current_temp, int rate_of_change)
{
    if (current_temp >= TEMP_CRITICAL || 
        (current_temp >= TEMP_WARNING && rate_of_change > 5))
    {
        return TEMP_CRITICAL_STATE;
    }
    else if (current_temp >= TEMP_WARNING)
    {
        return TEMP_WARNING_STATE;
    }
    else
    {
        return TEMP_NORMAL;
    }
}

Step 3: Import the Module and Analyse the Interface

Add temp_monitor.c to the TESSY project. TESSY performs automatic interface analysis:

• Inputs identified: current_temp (int), rate_of_change (int)
• Output identified: return value (TempStatus enum)
• No global variables accessed
• No called functions to stub

TESSY presents this interface in the test data editor, a tabular view with columns for each input and output variable.

Step 4: Design Test Cases

Open the test data editor for evaluate_temperature. Create test cases by adding rows to the table:

Test Case	current_temp	rate_of_change	Expected Return
TC1: Normal	50	2	TEMP_NORMAL
TC2: Warning, slow rise	85	3	TEMP_WARNING_STATE
TC3: Warning, fast rise	85	8	TEMP_CRITICAL_STATE
TC4: Critical temp	105	0	TEMP_CRITICAL_STATE
TC5: Boundary - warning	80	0	TEMP_WARNING_STATE
TC6: Boundary - critical	100	0	TEMP_CRITICAL_STATE
TC7: Just below warning	79	10	TEMP_NORMAL

Each row is a test case, TESSY will set the input values, call the function, and compare the actual return value against the expected value.

For a more systematic approach, use the Classification Tree Editor: define equivalence classes for current_temp (below warning, warning zone, critical zone) and rate_of_change (low, medium, high), then generate test vectors from the combination matrix. The CTE ensures you cover boundary values and edge cases systematically.

Step 5: Execute Tests

Click the execute button (or press the keyboard shortcut). TESSY:

1. Generates the test driver code (harness that calls evaluate_temperature with each test case’s inputs)
2. Compiles the test driver + source module with your cross-compiler
3. Executes the compiled test binary (on host simulator or on target via SEGGER J-Link)
4. Captures results and compares actual outputs against expected values
5. Measures code coverage

Execution takes seconds for a simple module. Results appear in the test data editor, green for passed test cases, red for failures.

Step 6: View Coverage Report

Open the coverage view. TESSY displays the source code with colour-coded annotations:

• Green lines: statements and branches that were executed
• Red lines: statements and branches that were not executed
• Condition-level highlighting: for MC/DC, each atomic condition is highlighted to show whether it has been independently demonstrated to affect the decision outcome

For our example function, the seven test cases should achieve high MC/DC coverage. The compound condition (current_temp >= TEMP_CRITICAL || (current_temp >= TEMP_WARNING && rate_of_change > 5)) has three atomic conditions, and our test cases exercise each one independently.

If any conditions are red, TESSY shows which specific combinations are missing, add targeted test cases to close the gaps.

Step 7: Generate Reports

TESSY generates reports in HTML and PDF formats:

• Test case report: all test cases with inputs, expected outputs, actual outputs, and pass/fail status
• Coverage report: statement, branch, decision, and MC/DC coverage percentages with annotated source code
• Requirements traceability: if requirements are linked (via ReqIF import), the report shows which requirements are verified by which test cases

These reports are suitable for inclusion in an ISO 26262 safety case or DO-178C certification package.

Next Steps

This tutorial covered the basic workflow on a simple module. For real project evaluation:

1. Import your actual firmware module: a safety-critical function from your current project
2. Configure your production compiler: test with the same toolchain you ship
3. Try on-target execution: connect a SEGGER J-Link and run tests on your hardware
4. Set up CI/CD: integrate TESSY into your Jenkins or GitLab pipeline for automated regression testing

Why Buy from GSAS

GSAS Micro Systems is the authorized Razorcat partner, providing TESSY evaluation licenses, onboarding training, and hands-on proof-of-concept support. Our engineers in Bengaluru, Hyderabad, Chennai, Pune, Mumbai, and Delhi NCR walk your team through the TESSY workflow on your actual codebase, not a contrived example, but your production firmware compiled with your toolchain on your target hardware.

Request a TESSY evaluation license →