diff --git a/backend/tests/test_blind_visibility.py b/backend/tests/test_blind_visibility.py
new file mode 100644
index 0000000..638c7ce
--- /dev/null
+++ b/backend/tests/test_blind_visibility.py
@@ -0,0 +1,129 @@
+"""Tests for red/blue blind visibility on GET /tests/{id}.
+
+Neither team should see the other team's data while a test is in
+draft/red_executing/red_review/blue_evaluating/blue_review. Both sides
+see everything once the test reaches in_review (and beyond). admin and
+viewer are never blinded.
+"""
+
+import uuid
+
+import pytest
+
+from app.models.evidence import Evidence
+from app.models.enums import TeamSide
+
+_RED_FIELDS = [
+    "procedure_text", "tool_used", "attack_success",
+    "execution_start_time", "execution_end_time", "red_summary",
+]
+_BLUE_FIELDS = [
+    "detection_result", "containment_result", "detection_time",
+    "containment_time", "blue_summary", "system_gaps",
+]
+
+
+def _add_evidence(db, test_id, team: TeamSide):
+    ev = Evidence(
+        test_id=uuid.UUID(test_id),
+        file_name="proof.txt",
+        file_path="s3://bucket/proof.txt",
+        sha256_hash="a" * 64,
+        team=team,
+    )
+    db.add(ev)
+    db.commit()
+
+
+@pytest.fixture
+def technique(api, auth_headers):
+    resp = api(
+        "post", "/api/v1/techniques", auth_headers,
+        json={"mitre_id": "T1059.100", "name": "Command Line"},
+    )
+    assert resp.status_code == 201, resp.text
+    return resp.json()["id"]
+
+
+@pytest.fixture
+def blind_test(client, db, api, auth_headers, red_tech_headers, technique):
+    """A test in red_executing with red-side content already filled in."""
+    resp = api(
+        "post", "/api/v1/tests", auth_headers,
+        json={"technique_id": technique, "name": "Blind visibility test"},
+    )
+    test_id = resp.json()["id"]
+
+    api("post", f"/api/v1/tests/{test_id}/start-execution", red_tech_headers)
+    api(
+        "patch", f"/api/v1/tests/{test_id}/red", red_tech_headers,
+        json={"procedure_text": "run mimikatz", "tool_used": "mimikatz", "red_summary": "dumped creds"},
+    )
+    return test_id
+
+
+def test_blue_viewer_cannot_see_red_fields_during_red_executing(
+    client, db, api, blind_test, blue_tech_headers
+):
+    resp = api("get", f"/api/v1/tests/{blind_test}", blue_tech_headers)
+    assert resp.status_code == 200
+    body = resp.json()
+    for field in _RED_FIELDS:
+        assert body[field] is None, f"{field} should be hidden from blue viewer"
+
+
+def test_red_viewer_cannot_see_blue_fields_during_red_executing(
+    client, db, api, blind_test, red_tech_headers
+):
+    resp = api("get", f"/api/v1/tests/{blind_test}", red_tech_headers)
+    assert resp.status_code == 200
+    body = resp.json()
+    for field in _BLUE_FIELDS:
+        assert body[field] is None, f"{field} should be hidden from red viewer"
+    # Red's own fields ARE visible to red
+    assert body["procedure_text"] == "run mimikatz"
+
+
+def test_admin_sees_everything_during_blind_states(
+    client, db, api, blind_test, auth_headers
+):
+    resp = api("get", f"/api/v1/tests/{blind_test}", auth_headers)
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["procedure_text"] == "run mimikatz"
+
+
+def test_both_sides_see_everything_once_in_review(
+    client, db, api, auth_headers, red_tech_headers, red_lead_headers,
+    blue_tech_headers, blue_lead_headers, red_lead_user, blue_lead_user, blind_test,
+):
+    test_id = blind_test
+    _add_evidence(db, test_id, TeamSide.red)
+    submit_red = api("post", f"/api/v1/tests/{test_id}/submit-red", red_tech_headers)
+    assert submit_red.status_code == 200, submit_red.text
+
+    approve_red = api("post", f"/api/v1/tests/{test_id}/review-red", red_lead_headers, json={"decision": "approve"})
+    assert approve_red.status_code == 200, approve_red.text
+
+    api("post", f"/api/v1/tests/{test_id}/start-blue-work", blue_tech_headers)
+    api(
+        "patch", f"/api/v1/tests/{test_id}/blue", blue_tech_headers,
+        json={"detection_result": "detected", "blue_summary": "caught it"},
+    )
+    _add_evidence(db, test_id, TeamSide.blue)
+    submit_blue = api("post", f"/api/v1/tests/{test_id}/submit-blue", blue_tech_headers)
+    assert submit_blue.status_code == 200, submit_blue.text
+
+    approve_blue = api("post", f"/api/v1/tests/{test_id}/review-blue", blue_lead_headers, json={"decision": "approve"})
+    assert approve_blue.status_code == 200, approve_blue.text
+    assert approve_blue.json()["state"] == "in_review"
+
+    resp_as_red = api("get", f"/api/v1/tests/{test_id}", red_tech_headers)
+    body_red = resp_as_red.json()
+    assert body_red["detection_result"] == "detected"
+    assert body_red["blue_summary"] == "caught it"
+
+    resp_as_blue = api("get", f"/api/v1/tests/{test_id}", blue_tech_headers)
+    body_blue = resp_as_blue.json()
+    assert body_blue["procedure_text"] == "run mimikatz"
+    assert body_blue["red_summary"] == "dumped creds"