TST: Add acceptance tests for 3DOF flight simulation

[Copilot]

Pull request type

• Code maintenance (refactoring, formatting, tests)

Checklist

• Tests for the changes have been added (if needed)
• Lint (black rocketpy/ tests/) has passed locally
• All tests (pytest tests -m slow --runslow) have passed locally

Current behavior

No acceptance tests exist for 3DOF flight simulation feature. Integration tests exist but lack end-to-end validation with realistic scenarios.

New behavior

Adds comprehensive acceptance test suite (tests/acceptance/test_3dof_flight.py) with 12 tests covering:

• Trajectory validation: Apogee, velocity, flight time within expected ranges
• Energy conservation: Kinetic/potential energy behavior through flight phases
• Weathercocking: Attitude evolution with coefficients 0.0, 0.5, 1.0, 2.0
• Mass variation: Propellant consumption and post-burnout behavior
• Reproducibility: Identical inputs yield identical outputs

Tests use realistic fixtures (127mm rocket, 1500N thrust, 3.5s burn) and gracefully skip when PointMassMotor/PointMassRocket are unavailable. Will auto-activate when #882 merges.

Fixture Organization: All 3DOF-specific fixtures have been centralized in tests/fixtures/flight/flight_fixtures.py for better reusability:

• acceptance_point_mass_motor: Realistic point mass motor fixture
• acceptance_point_mass_rocket: Point mass rocket fixture
• flight_3dof_no_weathercock: 3DOF flight without weathercocking
• flight_3dof_with_weathercock: 3DOF flight with weathercocking enabled

The fixtures reuse existing example_spaceport_env from environment_fixtures.py instead of creating duplicate environment fixtures.

Example test structure:

def test_3dof_weathercocking_affects_trajectory(
    flight_3dof_no_weathercock, flight_3dof_with_weathercock
):
    apogee_no_wc = flight_no_wc.apogee - flight_no_wc.env.elevation
    apogee_with_wc = flight_with_wc.apogee - flight_with_wc.env.elevation
    assert abs(apogee_no_wc - apogee_with_wc) > 0.1

Breaking change

• No

Additional information

Tests currently skip due to missing 3DOF classes. All existing acceptance tests (bella_lui, ndrt_2020, prometheus) pass unchanged. CodeQL: 0 alerts.

Fixtures have been properly organized following the project's pattern of centralizing test fixtures in tests/fixtures/ directory, improving code maintainability and reusability.

Original prompt

create a new branch: tst/3dof-acceptance-test which implements and solves the following Issue: #887. Also open a new PR with base branch as develop.

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[aZira371]

@copilot Please check if the fixtures from flight_fixtures.py can be reused for these tests or not. If yes then reuse them here. If not then add new fixtures to the flight_fixtures.py file.

[Copilot]

@copilot Please check if the fixtures from flight_fixtures.py can be reused for these tests or not. If yes then reuse them here. If not then add new fixtures to the flight_fixtures.py file.

Done! I've refactored the fixtures as requested:

Changes made (commit c6cbc90):

• ✅ Removed acceptance_environment fixture from test file
• ✅ Now reusing existing example_spaceport_env from environment_fixtures.py
• ✅ Moved all 3DOF-specific fixtures to flight_fixtures.py:
  • acceptance_point_mass_motor
  • acceptance_point_mass_rocket
  • flight_3dof_no_weathercock
  • flight_3dof_with_weathercock

Results:

• Test file reduced from 545 to 441 lines
• All fixtures now centralized in flight_fixtures.py for better reusability
• Fixtures use conditional import so they only load when 3DOF classes are available