diff --git a/tests/test_obs_processor.py b/tests/test_obs_processor.py
index e69de29..7b8b23e 100644
--- a/tests/test_obs_processor.py
+++ b/tests/test_obs_processor.py
@@ -0,0 +1,88 @@
+import jax
+import jax.numpy as jnp
+
+from brittle_star_project.environment.obs_processing import create_obs_processor
+from brittle_star_project.environment.env_config import MorphMode, ObservationBoundsConfig
+
+
+obs_bounds = ObservationBoundsConfig().to_bounds_dict()
+
+"""
+Test for obs_processor.
+
+Centralized: 40 features per agent:
+    disk_z_tilt              → scalar → reshaped to (1,)  → 1 feat
+    joint_actuator_force     → 8 joints padded to 8       → 8 feat
+    joint_position           → 8 joints padded to 8       → 8 feat
+    joint_velocity           → 8 joints padded to 8       → 8 feat
+    robot_direction_to_target→ (x, y)                     → 2 feat
+    segment_contact          → 4 segs, pre-padded by 9    → 13 feat (9 leading + 4)
+"""
+
+NUM_ARMS = 5
+SEGS_PER_ARM = 4  # healthy segments per arm
+JOINTS_PER_SEG = 2  # from _build_joint_indices: segs * 2
+
+SEGS_HEALTHY = [4, 4, 4, 4, 4]
+SEGS_DAMAGED = [4, 4, 4, 4, 0]  # arm 4 fully disabled
+AGENT_INDICES = [0, 1, 2, 3, 4]
+
+FEAT_PER_AGENT = 1 + 8 + 8 + 8 + 2 + 13  # = 40
+
+
+def make_obs(segs_per_arm: list[int]) -> dict:
+    total_segs = sum(segs_per_arm)
+    total_joints = JOINTS_PER_SEG * total_segs
+
+    return {
+        "actuator_force": jnp.ones(total_joints),
+        "disk_angular_velocity": jnp.zeros(3),
+        "disk_linear_velocity": jnp.zeros(3),
+        "disk_position": jnp.zeros(3),
+        "disk_rotation": jnp.array([0.1, 0.1, 0.5]),  # (roll, pitch, yaw)
+        "joint_actuator_force": jnp.full(total_joints, 1.0),
+        "joint_position": jnp.full(total_joints, 0.5),
+        "joint_velocity": jnp.full(total_joints, 2.0),
+        "segment_contact": jnp.ones(total_segs),
+        "tendon_position": jnp.zeros(0),
+        "tendon_velocity": jnp.zeros(0),
+        "unit_xy_direction_to_target": jnp.array([1.0, 0.0]),
+        "xy_distance_to_target": jnp.array([3.5]),
+    }
+
+
+def batch_obs(obs: dict):
+    return jax.tree_util.tree_map(lambda x: x[None, :], obs)
+
+
+def make_processor(morph_mode: MorphMode, segments_per_arm: list[int]):
+    return create_obs_processor(
+        bounds_dict=obs_bounds,
+        num_arms=NUM_ARMS,
+        needed_copies=NUM_ARMS,
+        morph_mode=morph_mode,
+        segments_per_arm=segments_per_arm,
+        agent_indices=AGENT_INDICES,
+    )
+
+
+def test_centralized_no_damage():
+    proc = make_processor(MorphMode.CENTRALIZED, SEGS_HEALTHY)
+    obs = make_obs(SEGS_HEALTHY)
+    obs = batch_obs(obs)
+    global_state = proc(obs)
+
+    # shape test
+    assert global_state.shape == (1, 1, FEAT_PER_AGENT * NUM_ARMS)
+
+
+def test_centralized_damaged_1_arm():
+    pass
+
+
+def test_decentralized_fully_connected_no_damage():
+    pass
+
+
+def test_decentralized_fully_connected_damaged_1_arm():
+    pass