diff --git a/tests/unittests/evaluation/test__eval_set_results_manager_utils.py b/tests/unittests/evaluation/test__eval_set_results_manager_utils.py
new file mode 100644
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+++ b/tests/unittests/evaluation/test__eval_set_results_manager_utils.py
@@ -0,0 +1,159 @@
+# Copyright 2026 Google LLC
+#
+# 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.
+
+from __future__ import annotations
+
+import json
+
+from google.adk.evaluation._eval_set_results_manager_utils import _sanitize_eval_set_result_name
+from google.adk.evaluation._eval_set_results_manager_utils import create_eval_set_result
+from google.adk.evaluation._eval_set_results_manager_utils import parse_eval_set_result_json
+from google.adk.evaluation.eval_metrics import EvalStatus
+from google.adk.evaluation.eval_result import EvalCaseResult
+from google.adk.evaluation.eval_result import EvalSetResult
+import pytest
+
+
+def _build_eval_case_result(
+    eval_id: str = "eval_1", session_id: str = "session_1"
+) -> EvalCaseResult:
+  """Builds a minimal but valid EvalCaseResult for testing."""
+  return EvalCaseResult(
+      eval_set_id="eval_set_1",
+      eval_id=eval_id,
+      final_eval_status=EvalStatus.PASSED,
+      overall_eval_metric_results=[],
+      eval_metric_result_per_invocation=[],
+      session_id=session_id,
+  )
+
+
+class TestSanitizeEvalSetResultName:
+
+  def test_replaces_forward_slash_with_underscore(self):
+    assert _sanitize_eval_set_result_name("app/eval_set") == "app_eval_set"
+
+  def test_replaces_all_forward_slashes(self):
+    assert _sanitize_eval_set_result_name("a/b/c/d") == "a_b_c_d"
+
+  def test_name_without_slash_is_unchanged(self):
+    assert _sanitize_eval_set_result_name("app_eval_set_123") == (
+        "app_eval_set_123"
+    )
+
+  def test_empty_name_is_unchanged(self):
+    assert _sanitize_eval_set_result_name("") == ""
+
+
+class TestCreateEvalSetResult:
+
+  def test_creates_eval_set_result_with_expected_fields(self):
+    eval_case_results = [_build_eval_case_result()]
+
+    result = create_eval_set_result(
+        app_name="my_app",
+        eval_set_id="my_eval_set",
+        eval_case_results=eval_case_results,
+    )
+
+    assert isinstance(result, EvalSetResult)
+    assert result.eval_set_id == "my_eval_set"
+    assert result.eval_case_results == eval_case_results
+
+  def test_result_id_encodes_app_eval_set_and_timestamp(self):
+    result = create_eval_set_result(
+        app_name="my_app",
+        eval_set_id="my_eval_set",
+        eval_case_results=[],
+    )
+
+    # The id is "{app_name}_{eval_set_id}_{timestamp}" and the timestamp is
+    # stored verbatim as the creation_timestamp.
+    assert result.eval_set_result_id == (
+        f"my_app_my_eval_set_{result.creation_timestamp}"
+    )
+
+  def test_result_name_is_sanitized(self):
+    # A "/" in the id (here via the app name) must not survive into the name,
+    # since the name is used to derive a filesystem-safe identifier.
+    result = create_eval_set_result(
+        app_name="my/app",
+        eval_set_id="my_eval_set",
+        eval_case_results=[],
+    )
+
+    assert "/" not in result.eval_set_result_name
+    assert result.eval_set_result_name == (
+        result.eval_set_result_id.replace("/", "_")
+    )
+
+  def test_creates_result_with_empty_eval_case_results(self):
+    result = create_eval_set_result(
+        app_name="my_app",
+        eval_set_id="my_eval_set",
+        eval_case_results=[],
+    )
+
+    assert result.eval_case_results == []
+
+
+class TestParseEvalSetResultJson:
+
+  def _build_eval_set_result(self) -> EvalSetResult:
+    return EvalSetResult(
+        eval_set_result_id="my_app_my_eval_set_123.0",
+        eval_set_result_name="my_app_my_eval_set_123.0",
+        eval_set_id="my_eval_set",
+        eval_case_results=[_build_eval_case_result()],
+        creation_timestamp=123.0,
+    )
+
+  def test_parses_standard_json_string(self):
+    original = self._build_eval_set_result()
+
+    parsed = parse_eval_set_result_json(original.model_dump_json())
+
+    assert parsed == original
+
+  def test_parses_json_bytes(self):
+    original = self._build_eval_set_result()
+
+    parsed = parse_eval_set_result_json(original.model_dump_json().encode())
+
+    assert parsed == original
+
+  def test_parses_camel_case_aliased_json(self):
+    original = self._build_eval_set_result()
+
+    parsed = parse_eval_set_result_json(original.model_dump_json(by_alias=True))
+
+    assert parsed == original
+
+  def test_parses_legacy_double_encoded_json(self):
+    # Legacy result files stored the object as a JSON-encoded string, i.e. the
+    # outer JSON is a string whose value is itself the inner JSON object.
+    original = self._build_eval_set_result()
+    double_encoded = json.dumps(original.model_dump_json())
+
+    parsed = parse_eval_set_result_json(double_encoded)
+
+    assert parsed == original
+
+  def test_raises_on_json_object_missing_required_fields(self):
+    with pytest.raises(Exception):
+      parse_eval_set_result_json('{"unexpected_field": "value"}')
+
+  def test_raises_on_non_json_input(self):
+    with pytest.raises(Exception):
+      parse_eval_set_result_json("not valid json at all {")