code: def basis_representation_test_data(self):
      data = [
          dict(
              matrix_representation=gs.array(
                  [[1.0, 0.0, 0.0], [0.6, 7.0, 0.0], [-3.0, 0.0, 8.0]]
              ),
              expected=gs.array([1.0, 0.6, 7.0, -3.0, 0.0, 8.0]),
          ),
      ]
      return self.generate_tests(data)
  
file_path: geomstats/tests/tests_geomstats/test_geometry/data/lower_triangular_matrices.py
imports: import geomstats.backend
  from geomstats.test.data import TestData
  from .base import MatrixVectorSpaceTestData
label_desc: Use image node_id 2 for calling the LowerTriangularMatrices3TestData obj's underlying member method code with example usage: obj.basis_representation_test_data() and returns: self