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lerobot/tests/rewards/test_distributional_value_function.py
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Khalil Meftah d0348b1803 refactor(rewards): rewrite distributional VF with SigLIP2 + Gemma3 backbone
Replace PaliGemma-based value function with a monolithic VLM architecture
using SigLIP2-so400m (vision encoder) and Gemma3-270M (shared backbone),
matching the pi*0.6 paper.

Key changes:
- SigLIP2-so400m as vision encoder, Gemma3-270M as unified transformer
- [CLS] token readout with bidirectional prefix attention
- 2-layer MLP value head (Linear -> LayerNorm -> GELU -> Dropout -> Linear)
- Multi-camera support with per-camera validity masks
- Image preprocessing in processor (resize with pad, normalize to [-1,1])
- Freeze controls for vision encoder and language model independently
2026-07-18 19:31:03 +02:00

718 lines
24 KiB
Python

# Copyright 2025 The HuggingFace Inc. team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Tests for RECAP's distributional value function."""
from __future__ import annotations
import pytest
import torch
from lerobot.configs.rewards import RewardModelConfig
from lerobot.configs.types import FeatureType, NormalizationMode, PolicyFeature
from lerobot.rewards.distributional_value_function.configuration_distributional_value_function import (
DistributionalVFConfig,
)
from lerobot.types import TransitionKey
from lerobot.utils.constants import OBS_IMAGES
from tests.utils import skip_if_package_missing
BATCH_SIZE = 4
NUM_BINS = 201
IMAGE_KEY = f"{OBS_IMAGES}.top"
IMAGE_KEY_WRIST_LEFT = f"{OBS_IMAGES}.wrist_left"
IMAGE_KEY_WRIST_RIGHT = f"{OBS_IMAGES}.wrist_right"
def _make_config(**overrides) -> DistributionalVFConfig:
defaults = {
"device": "cpu",
"image_resolution": (224, 224),
}
defaults.update(overrides)
config = DistributionalVFConfig(**defaults)
config.input_features = {
IMAGE_KEY: PolicyFeature(type=FeatureType.VISUAL, shape=(3, 224, 224)),
IMAGE_KEY_WRIST_LEFT: PolicyFeature(type=FeatureType.VISUAL, shape=(3, 224, 224)),
IMAGE_KEY_WRIST_RIGHT: PolicyFeature(type=FeatureType.VISUAL, shape=(3, 224, 224)),
}
config.output_features = {}
config.normalization_mapping = {
"VISUAL": NormalizationMode.IDENTITY,
}
return config
def _make_model():
from lerobot.rewards.distributional_value_function.modeling_distributional_value_function import (
DistributionalVFRewardModel,
)
return DistributionalVFRewardModel(_make_config())
def _make_batch(batch_size: int = BATCH_SIZE, device: str = "cpu") -> dict[str, torch.Tensor]:
from lerobot.rewards.distributional_value_function.processor_distributional_value_function import (
IMAGE_MASK_SUFFIX,
)
from lerobot.utils.constants import OBS_LANGUAGE_ATTENTION_MASK, OBS_LANGUAGE_TOKENS
return {
IMAGE_KEY: torch.rand(batch_size, 3, 224, 224, device=device) * 2 - 1,
IMAGE_KEY + IMAGE_MASK_SUFFIX: torch.ones(batch_size, dtype=torch.bool, device=device),
IMAGE_KEY_WRIST_LEFT: torch.rand(batch_size, 3, 224, 224, device=device) * 2 - 1,
IMAGE_KEY_WRIST_LEFT + IMAGE_MASK_SUFFIX: torch.ones(batch_size, dtype=torch.bool, device=device),
IMAGE_KEY_WRIST_RIGHT: torch.rand(batch_size, 3, 224, 224, device=device) * 2 - 1,
IMAGE_KEY_WRIST_RIGHT + IMAGE_MASK_SUFFIX: torch.ones(batch_size, dtype=torch.bool, device=device),
OBS_LANGUAGE_TOKENS: torch.randint(0, 1000, (batch_size, 200), device=device),
OBS_LANGUAGE_ATTENTION_MASK: torch.ones(batch_size, 200, dtype=torch.bool, device=device),
"mc_return": torch.rand(batch_size, device=device) * -1.0,
"is_terminal": torch.zeros(batch_size, dtype=torch.bool, device=device),
}
# ------------------------------------------------------------------
# Config / registry tests
# ------------------------------------------------------------------
def test_config_registered_in_reward_model_registry():
"""DistributionalVFConfig is discoverable via RewardModelConfig registry."""
known = RewardModelConfig.get_known_choices()
assert "distributional_value_function" in known
def test_factory_returns_correct_class():
"""get_reward_model_class returns DistributionalVFRewardModel."""
from lerobot.rewards.factory import get_reward_model_class
cls = get_reward_model_class("distributional_value_function")
from lerobot.rewards.distributional_value_function.modeling_distributional_value_function import (
DistributionalVFRewardModel,
)
assert cls is DistributionalVFRewardModel
def test_make_reward_model_config_factory():
"""make_reward_model_config creates DistributionalVFConfig with overrides."""
from lerobot.rewards.factory import make_reward_model_config
config = make_reward_model_config("distributional_value_function", num_value_bins=101)
assert isinstance(config, DistributionalVFConfig)
assert config.num_value_bins == 101
# ------------------------------------------------------------------
# Target distribution tests (HL-Gauss, Dirac delta, one-hot)
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_hl_gauss_sums_to_one():
"""HL-Gauss target distribution sums to 1 for each sample."""
model = _make_model()
targets = torch.tensor([-0.5, -0.1, -0.9, -0.0])
dist = model.hl_gauss_target(targets)
assert dist.shape == (4, NUM_BINS)
torch.testing.assert_close(dist.sum(dim=-1), torch.ones(4), atol=1e-5, rtol=0)
@skip_if_package_missing("transformers")
def test_hl_gauss_non_negative():
"""HL-Gauss target probabilities are all non-negative."""
model = _make_model()
targets = torch.linspace(-1.0, 0.0, 10)
dist = model.hl_gauss_target(targets)
assert (dist >= 0).all()
@skip_if_package_missing("transformers")
def test_hl_gauss_expected_value_matches():
"""E[V] under HL-Gauss distribution matches the target value."""
model = _make_model()
targets = torch.tensor([-0.5, -0.1, -0.9])
dist = model.hl_gauss_target(targets)
expected = (dist * model.value_head.bin_centers).sum(dim=-1)
torch.testing.assert_close(expected, targets, atol=1e-4, rtol=0)
@skip_if_package_missing("transformers")
def test_hl_gauss_handles_2d_input():
"""HL-Gauss handles [batch_size, 1] shaped inputs correctly."""
model = _make_model()
targets = torch.tensor([-0.5, -0.3]).unsqueeze(-1)
dist = model.hl_gauss_target(targets)
assert dist.shape == (2, NUM_BINS)
torch.testing.assert_close(dist.sum(dim=-1), torch.ones(2), atol=1e-5, rtol=0)
@skip_if_package_missing("transformers")
def test_dirac_delta_sums_to_one():
"""Dirac delta target distribution sums to 1 for each sample."""
model = _make_model()
targets = torch.tensor([-0.5, -0.1, -0.9, -1.0, 0.0])
dist = model.dirac_delta_target(targets)
assert dist.shape == (5, NUM_BINS)
torch.testing.assert_close(dist.sum(dim=-1), torch.ones(5), atol=1e-6, rtol=0)
@skip_if_package_missing("transformers")
def test_dirac_delta_at_most_two_nonzero():
"""Dirac delta places probability on at most two adjacent bins."""
model = _make_model()
targets = torch.tensor([-0.7523, -0.0013])
dist = model.dirac_delta_target(targets)
for i in range(2):
assert (dist[i] > 0).sum() <= 2
@skip_if_package_missing("transformers")
def test_dirac_delta_expected_value_matches():
"""E[V] under Dirac delta distribution matches the target value."""
model = _make_model()
targets = torch.tensor([-0.5, -0.1, -0.9])
dist = model.dirac_delta_target(targets)
expected = (dist * model.value_head.bin_centers).sum(dim=-1)
torch.testing.assert_close(expected, targets, atol=1e-5, rtol=0)
@skip_if_package_missing("transformers")
def test_dirac_delta_boundary_values_clamped():
"""Values outside support are clamped to boundary bins."""
model = _make_model()
targets = torch.tensor([-1.5, 0.5])
dist = model.dirac_delta_target(targets)
torch.testing.assert_close(dist.sum(dim=-1), torch.ones(2), atol=1e-6, rtol=0)
assert dist[0, 0] == 1.0
assert dist[1, -1] == 1.0
@skip_if_package_missing("transformers")
def test_one_hot_single_nonzero():
"""One-hot target has exactly one non-zero bin per sample."""
model = _make_model()
targets = torch.tensor([-0.5, -0.1, -1.0, 0.0])
dist = model.one_hot_target(targets)
assert dist.shape == (4, NUM_BINS)
for i in range(4):
assert (dist[i] > 0).sum() == 1
assert dist[i].sum() == 1.0
@skip_if_package_missing("transformers")
def test_one_hot_nearest_bin():
"""One-hot target activates the bin closest to the target value."""
model = _make_model()
targets = torch.tensor([-0.5])
dist = model.one_hot_target(targets)
hot_idx = dist[0].argmax()
assert model.value_head.bin_centers[hot_idx].item() == pytest.approx(-0.5, abs=0.003)
@skip_if_package_missing("transformers")
def test_terminal_gets_one_hot():
"""Terminal states receive one-hot targets; non-terminal get HL-Gauss."""
model = _make_model()
targets = torch.tensor([-0.5, -0.3, -0.7, -0.9])
is_terminal = torch.tensor([False, True, False, True])
dist = model.compute_target_distribution(
targets, is_terminal, method="hl_gauss", use_one_hot_terminal=True
)
for i in range(4):
assert dist[i].sum().item() == pytest.approx(1.0, abs=1e-5)
assert (dist[1] > 0).sum() == 1
assert (dist[3] > 0).sum() == 1
assert (dist[0] > 0).sum() > 2
assert (dist[2] > 0).sum() > 2
@skip_if_package_missing("transformers")
def test_no_terminal_override_when_disabled():
"""When use_one_hot_terminal=False, terminal states use the base method."""
model = _make_model()
targets = torch.tensor([-0.5, -0.3])
is_terminal = torch.tensor([False, True])
dist = model.compute_target_distribution(
targets, is_terminal, method="hl_gauss", use_one_hot_terminal=False
)
assert (dist[1] > 0).sum() > 2
# ------------------------------------------------------------------
# Architecture / component tests
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_model_has_expected_components():
"""Model scaffold contains the SigLIP2+Gemma3+ValueHead components."""
model = _make_model()
assert hasattr(model, "vision_encoder")
assert hasattr(model, "gemma3")
assert hasattr(model, "image_proj")
assert hasattr(model, "value_head")
assert hasattr(model, "cls_embedding")
assert hasattr(model.value_head, "mlp")
assert hasattr(model.value_head, "bin_centers")
@skip_if_package_missing("transformers")
def test_model_bin_centers_shape():
"""Value head bin_centers buffer has shape (num_value_bins,)."""
model = _make_model()
assert model.value_head.bin_centers.shape == (NUM_BINS,)
@skip_if_package_missing("transformers")
def test_value_head_output_dim():
"""Value head linear projection outputs num_value_bins logits."""
model = _make_model()
assert model.value_head.mlp[-1].out_features == NUM_BINS
@skip_if_package_missing("transformers")
def test_cls_embedding_is_nn_embedding():
"""CLS is nn.Embedding (FSDP-safe) with correct shape."""
model = _make_model()
from torch import nn
assert isinstance(model.cls_embedding, nn.Embedding)
assert model.cls_embedding.num_embeddings == 1
assert model.cls_embedding.embedding_dim == model.gemma3_hidden
@skip_if_package_missing("transformers")
def test_image_proj_dimensions():
"""Image projection maps SigLIP2 hidden to Gemma3 hidden."""
model = _make_model()
siglip_hidden = model.vision_encoder.config.hidden_size
assert model.image_proj.in_features == siglip_hidden
assert model.image_proj.out_features == model.gemma3_hidden
# ------------------------------------------------------------------
# Forward / inference tests
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_forward_returns_loss_and_dict():
"""Forward pass returns a finite scalar loss and output dict with expected keys."""
model = _make_model()
batch = _make_batch()
loss, output_dict = model.forward(batch)
assert loss.shape == ()
assert torch.isfinite(loss)
assert "loss" in output_dict
assert "predicted_value_mean" in output_dict
assert "mc_return_mean" in output_dict
assert "acc_best" in output_dict
assert "acc_neighbor" in output_dict
assert "mae" in output_dict
@skip_if_package_missing("transformers")
def test_forward_loss_is_positive():
"""Cross-entropy loss is strictly positive for random weights."""
model = _make_model()
batch = _make_batch()
loss, _ = model.forward(batch)
assert loss.item() > 0
@skip_if_package_missing("transformers")
def test_compute_reward_returns_correct_shape():
"""compute_reward returns [batch_size] tensor of finite float32 values."""
model = _make_model()
model.eval()
batch = _make_batch(batch_size=3)
with torch.no_grad():
values = model.compute_reward(batch)
assert values.shape == (3,)
assert values.dtype == torch.float32
assert torch.isfinite(values).all()
@skip_if_package_missing("transformers")
def test_compute_reward_values_in_support_range():
"""Predicted values lie within [value_support_min, value_support_max]."""
model = _make_model()
model.eval()
batch = _make_batch(batch_size=8)
with torch.no_grad():
values = model.compute_reward(batch)
assert (values >= -1.0 - 0.01).all()
assert (values <= 0.0 + 0.01).all()
# ------------------------------------------------------------------
# Gradient flow tests
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_gradient_flows_through_value_head():
"""Backprop produces non-zero gradients on the value head projection."""
model = _make_model()
model.train()
batch = _make_batch()
loss, _ = model.forward(batch)
loss.backward()
assert model.value_head.mlp[-1].weight.grad is not None
assert not torch.all(model.value_head.mlp[-1].weight.grad == 0)
@skip_if_package_missing("transformers")
def test_gradient_flows_through_cls_embedding():
"""Backprop produces non-zero gradients on the learned [CLS] embedding."""
model = _make_model()
model.train()
batch = _make_batch()
loss, _ = model.forward(batch)
loss.backward()
assert model.cls_embedding.weight.grad is not None
assert not torch.all(model.cls_embedding.weight.grad == 0)
@skip_if_package_missing("transformers")
def test_gradient_flows_through_image_proj():
"""Backprop produces non-zero gradients on the image projection."""
model = _make_model()
model.train()
batch = _make_batch()
loss, _ = model.forward(batch)
loss.backward()
assert model.image_proj.weight.grad is not None
assert not torch.all(model.image_proj.weight.grad == 0)
# ------------------------------------------------------------------
# Freeze / training infrastructure tests
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_freeze_vision_encoder():
"""freeze_vision_encoder disables requires_grad on SigLIP2."""
model = _make_model()
model.config.freeze_vision_encoder = True
model._set_requires_grad()
for p in model.vision_encoder.parameters():
assert not p.requires_grad
for p in model.value_head.parameters():
assert p.requires_grad
@skip_if_package_missing("transformers")
def test_freeze_language_model():
"""freeze_language_model disables requires_grad on Gemma3."""
model = _make_model()
model.config.freeze_language_model = True
model._set_requires_grad()
for p in model.gemma3.parameters():
assert not p.requires_grad
for p in model.value_head.parameters():
assert p.requires_grad
@skip_if_package_missing("transformers")
def test_stop_gradient_to_vlm_preserves_cls_grad():
"""With stop_gradient_to_vlm, CLS embedding still gets gradients."""
config = _make_config(stop_gradient_to_vlm=True)
from lerobot.rewards.distributional_value_function.modeling_distributional_value_function import (
DistributionalVFRewardModel,
)
model = DistributionalVFRewardModel(config)
model.train()
batch = _make_batch()
loss, _ = model.forward(batch)
loss.backward()
assert model.cls_embedding.weight.grad is not None
assert not torch.all(model.cls_embedding.weight.grad == 0)
# ------------------------------------------------------------------
# Config validation tests
# ------------------------------------------------------------------
def test_config_requires_visual_feature():
"""validate_features raises if no VISUAL feature is present."""
config = DistributionalVFConfig()
config.input_features = {
"observation.state": PolicyFeature(type=FeatureType.STATE, shape=(14,)),
}
with pytest.raises(ValueError, match="VISUAL"):
config.validate_features()
def test_config_passes_with_visual_feature():
"""validate_features succeeds when a VISUAL feature is present."""
config = _make_config()
config.validate_features()
# ------------------------------------------------------------------
# Processor tests
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_processor_pipeline_produces_expected_keys():
"""Full preprocessor pipeline produces tokenized text, preprocessed images, and masks."""
from lerobot.rewards.distributional_value_function.processor_distributional_value_function import (
IMAGE_MASK_SUFFIX,
make_distributional_vf_pre_post_processors,
)
from lerobot.utils.constants import OBS_LANGUAGE_ATTENTION_MASK, OBS_LANGUAGE_TOKENS
config = _make_config()
preprocessor, _ = make_distributional_vf_pre_post_processors(config)
raw_batch = {
IMAGE_KEY: torch.rand(3, 224, 224),
IMAGE_KEY_WRIST_LEFT: torch.rand(3, 224, 224),
IMAGE_KEY_WRIST_RIGHT: torch.rand(3, 224, 224),
"task": "pick up the cup",
}
processed = preprocessor(raw_batch)
assert OBS_LANGUAGE_TOKENS in processed
assert OBS_LANGUAGE_ATTENTION_MASK in processed
assert IMAGE_KEY in processed
assert IMAGE_KEY + IMAGE_MASK_SUFFIX in processed
assert IMAGE_KEY_WRIST_LEFT + IMAGE_MASK_SUFFIX in processed
assert IMAGE_KEY_WRIST_RIGHT + IMAGE_MASK_SUFFIX in processed
img = processed[IMAGE_KEY]
assert img.shape == (1, 3, 224, 224)
assert img.min() >= -1.0 - 1e-5
assert img.max() <= 1.0 + 1e-5
def test_task_prompt_formats_correctly():
"""Task prompt step builds 'Task: {task}.' format."""
from lerobot.rewards.distributional_value_function.processor_distributional_value_function import (
DistributionalVFPrepareTaskPromptStep,
)
step = DistributionalVFPrepareTaskPromptStep()
transition = {
TransitionKey.COMPLEMENTARY_DATA: {"task": ["pick_up_the_cup"]},
}
result = step(transition)
prompt = result[TransitionKey.COMPLEMENTARY_DATA]["task"][0]
assert prompt == "Task: pick up the cup."
def test_task_prompt_handles_string_input():
"""Task prompt step accepts a plain string task."""
from lerobot.rewards.distributional_value_function.processor_distributional_value_function import (
DistributionalVFPrepareTaskPromptStep,
)
step = DistributionalVFPrepareTaskPromptStep()
transition = {
TransitionKey.COMPLEMENTARY_DATA: {"task": "open_drawer"},
}
result = step(transition)
prompt = result[TransitionKey.COMPLEMENTARY_DATA]["task"][0]
assert prompt == "Task: open drawer."
def test_task_prompt_raises_on_missing_task():
"""Task prompt step raises ValueError when task key is absent."""
from lerobot.rewards.distributional_value_function.processor_distributional_value_function import (
DistributionalVFPrepareTaskPromptStep,
)
step = DistributionalVFPrepareTaskPromptStep()
transition = {
TransitionKey.COMPLEMENTARY_DATA: {},
}
with pytest.raises(ValueError, match="No task found"):
step(transition)
def test_image_preprocessor_resize_and_normalize():
"""Image preprocessor resizes, normalizes to [-1,1], and adds masks."""
from lerobot.rewards.distributional_value_function.processor_distributional_value_function import (
IMAGE_MASK_SUFFIX,
DistributionalVFImagePreprocessorStep,
)
step = DistributionalVFImagePreprocessorStep(
image_resolution=(224, 224),
image_keys=(IMAGE_KEY,),
)
transition = {
TransitionKey.OBSERVATION: {
IMAGE_KEY: torch.rand(2, 3, 320, 240), # non-square, [0, 1]
}
}
result = step(transition)
obs = result[TransitionKey.OBSERVATION]
assert obs[IMAGE_KEY].shape == (2, 3, 224, 224)
assert obs[IMAGE_KEY].min() >= -1.0 - 1e-5
assert obs[IMAGE_KEY].max() <= 1.0 + 1e-5
assert obs[IMAGE_KEY + IMAGE_MASK_SUFFIX].all()
def test_image_preprocessor_missing_camera_gets_placeholder():
"""Missing cameras get black placeholder and mask=False."""
from lerobot.rewards.distributional_value_function.processor_distributional_value_function import (
IMAGE_MASK_SUFFIX,
DistributionalVFImagePreprocessorStep,
)
step = DistributionalVFImagePreprocessorStep(
image_resolution=(224, 224),
image_keys=(IMAGE_KEY, IMAGE_KEY_WRIST_LEFT),
)
transition = {
TransitionKey.OBSERVATION: {
IMAGE_KEY: torch.rand(2, 3, 224, 224),
}
}
result = step(transition)
obs = result[TransitionKey.OBSERVATION]
assert obs[IMAGE_KEY + IMAGE_MASK_SUFFIX].all()
assert not obs[IMAGE_KEY_WRIST_LEFT + IMAGE_MASK_SUFFIX].any()
assert obs[IMAGE_KEY_WRIST_LEFT].shape == (2, 3, 224, 224)
# ------------------------------------------------------------------
# Save / load roundtrip
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_save_load_pretrained_roundtrip(tmp_path):
"""Saved model can be loaded back with identical weights."""
from lerobot.rewards.distributional_value_function.modeling_distributional_value_function import (
DistributionalVFRewardModel,
)
model = _make_model()
model._save_pretrained(tmp_path)
loaded = DistributionalVFRewardModel.from_pretrained(str(tmp_path))
orig_sd = model.state_dict()
loaded_sd = loaded.state_dict()
assert set(orig_sd.keys()) == set(loaded_sd.keys())
for key in orig_sd:
torch.testing.assert_close(orig_sd[key], loaded_sd[key], msg=f"Mismatch in {key}")
# ------------------------------------------------------------------
# Attention mask utility test
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_make_att_2d_masks():
"""Verify attention mask construction for prefix + CLS."""
from lerobot.rewards.distributional_value_function.modeling_distributional_value_function import (
make_att_2d_masks,
)
pad = torch.ones(1, 4, dtype=torch.bool)
att = torch.tensor([[0, 0, 0, 1]])
mask = make_att_2d_masks(pad, att)[0]
assert mask[0, 0] # prefix sees prefix
assert mask[1, 2] # prefix sees prefix
assert not mask[0, 3] # prefix does NOT see CLS
assert mask[3, 0] # CLS sees prefix
assert mask[3, 3] # CLS sees itself
# ------------------------------------------------------------------
# Categorical metrics test
# ------------------------------------------------------------------
@skip_if_package_missing("transformers")
def test_categorical_metrics_perfect_prediction():
"""Metrics return acc_best=1 when logits peak at the correct bin."""
model = _make_model()
bin_centers = model.value_head.bin_centers
target = bin_centers[100].unsqueeze(0) # exact bin center
batch = _make_batch(batch_size=1)
batch["mc_return"] = target
batch["is_terminal"] = torch.zeros(1, dtype=torch.bool)
with torch.no_grad():
_, output_dict = model.forward(batch)
assert "acc_best" in output_dict
assert "acc_neighbor" in output_dict
assert "mae" in output_dict
assert isinstance(output_dict["acc_best"], float)
assert isinstance(output_dict["mae"], float)