PreRunModifier

A PreRunModifier can modify the test suite before it is executed.
It is like a "dry run" of the test suite with the possibility to modify the test suite before the actual execution.
It can be enabled by using the --prerunmodifier option when running the test suite.

Things you can do with a PreRunModifier:

• Skip or filter tests
• Read or modify test data (e.g. variables, tags, ...)
• Read or modify tests
• Read or modify keywords
• ...

Check out the Robot Framework User Guide for more information.

Visitor

Pre-run modifiers should be implemented as visitors that can traverse through the executable test suite structure and modify it as needed. The visitor interface is explained as part of the Robot Framework API documentation, and it possible to modify executed test suites, test cases and keywords using it

The visitor interface can execute code on the following events:

• visit_suite
• start_suite
• end_suite
• visit_test
• start_test
• end_test
• visit_keyword
• start_keyword
• end_keyword

This is only a subset of the events that are available, but it is the most common ones.
Check out the Robot Framework API documentation for more information.

Robot Model

The Robot Framework API provides different objects that represent Robot Framework data.
Depending on the event, the visitor will receive a different object.
The following table shows the different objects that are available for each event.

Event	Object
visit_suite/start_suite/end_suite	Testsuite
visit_test/start_test/end_test	Testcase
visit_keyword/start_keyword/end_keyword	Keyword

Again, this is only a subset of the objects that are available, but it is the most common ones.

Test Suite

The Testsuite object represents a test suite.

The following properties are available:

Property	Description
id	Unique ID of the test suite
name	Name of the test suite
source	Path to the test suite file
doc	Documentation of the test suite
metadata	Metadata of the test suite
tests	List of tests in the test suite
suites	List of child test suites
setup	Setup of the test suite
teardown	Teardown of the test suite
test_count	Number of tests in the test suite
parent	Parent test suite
keywords	List of keywords in the test suite

As the test suite is a container for tests and other test suites, it is possible to access and modify the tests and suites objects from a top level test suite directly.

Read Test Names from Test Suite

The following example shows how to read the names of all tests in a test suite.

ReadTestNames.py

"""Pre-run modifier that reads the names of all tests in a test suite."""

from robot.api import SuiteVisitor

def start_suite(self, suite):
    """Read the names of all tests in the test suite."""
    for test in suite.tests:
        print(test.name)

Example

Select every Xth test

This example shows how to select every Xth test in a test suite.
It could be used to distribute tests across multiple test runners, where each test runner only executes a subset of the tests.

SelectEveryXthTest.py

"""Pre-run modifier that selects only every Xth test for execution.

Starts from the first test by default. Tests are selected per suite.
"""

from robot.api import SuiteVisitor


class SelectEveryXthTest(SuiteVisitor):

    def __init__(self, x: int, start: int = 0):
        self.x = x
        self.start = start

    def start_suite(self, suite):
        """Modify suite's tests to contain only every Xth."""
        suite.tests = suite.tests[self.start::self.x]

    def end_suite(self, suite):
        """Remove suites that are empty after removing tests."""
        suite.suites = [s for s in suite.suites if s.test_count > 0]

    def visit_test(self, test):
        """Avoid visiting tests and their keywords to save a little time."""
        pass

The command below will select every third test in the test suite, starting from the first test.

robot --prerunmodifier SelectEveryXthTest:3:0 tests

To distribute the tests across three test runners, you would need to run

# Test Runner 1
robot --prerunmodifier SelectEveryXthTest:3:0 tests
# Test Runner 2
robot --prerunmodifier SelectEveryXthTest:3:1 tests
# Test Runner 3
robot --prerunmodifier SelectEveryXthTest:3:2 tests

Copy and Modify Tests

The following example shows how to copy and modify tests in a test suite.

CopyTest.py

from robot.api import SuiteVisitor

class CopyTest(SuiteVisitor):
    def start_suite(self, suite):
        """Copy and modify tests in the test suite."""
        for test in suite.tests:
            if "copy" not in test.tags:
                test_case = suite.tests.append(test.copy())
                test_case.tags.add("copy")
                test_case.name = f"{test_case.name} (copy)"

6: Loop over all tests in the test suite
7: Check if the test does not have the tag "copy"
8: Copy the test and add it to the end of the test suite
9: Add the tag "copy" to the copied test
10: Modify the name of the copied test

robot --prerunmodifier CopyTest.py tests