Tests in bmm/src/tests/test_smc.py fail with AttributeError

[matt-graham]

Submitting as part of JOSS review openjournals/joss-reviews/issues/3651

Running

python bmm/src/tests/test_smc.py

results in two test failures in TestUpdateParticlesPF.test_update and TestUpdateParticlesBSi.test_update, in both cases due to similar AttributeError instances

Traceback (most recent call last):
  File "bmm/bmm/src/tests/test_smc.py", line 102, in test_update
    updated_particles = smc.update_particles_flbs(self.graph,
  File "bmm/bmm/src/inference/smc.py", line 250, in update_particles_flbs
    out_particles.time_intervals = np.append(out_particles.time_intervals, time_interval)
AttributeError: 'MMParticles' object has no attribute 'time_intervals'

Traceback (most recent call last):
  File "/bmm/bmm/src/tests/test_smc.py", line 102, in test_update
    updated_particles = smc.update_particles_flbs(self.graph,
  File "bmm/bmm/src/inference/smc.py", line 250, in update_particles_flbs
    out_particles.time_intervals = np.append(out_particles.time_intervals, time_interval)
AttributeError: 'MMParticles' object has no attribute 'time_intervals'

[SamDuffield]

Thanks - fixed to create an empty time_intervals if it hasn't been initiated yet (as is common at the start of a trip)

[matt-graham]

All tests now run successfully and pass for me.