diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 9b94b95..1e02aec 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -40,7 +40,7 @@ jobs:
 
       - name: Test with pytest
         run: |
-          pytest --cov --cov-report=xml --continue-on-collection-errors -n 4
+          pytest --cov --cov-report=xml --continue-on-collection-errors
 
       - name: Upload coverage reports to Codecov
         uses: codecov/codecov-action@v4
diff --git a/tests/test_cls.py b/tests/test_cls.py
index d7c888c..c57c41a 100644
--- a/tests/test_cls.py
+++ b/tests/test_cls.py
@@ -7,8 +7,8 @@
 
 def get_adata() -> sc.AnnData:
     adata = sc.datasets.visium_sge("V1_Breast_Cancer_Block_A_Section_1")
-    # random sample 500 cells
-    # adata = adata[np.random.choice(adata.obs.index, 500), :].copy()
+    # sample first 500 cells
+    adata = adata[:500, :]
     adata.layers["counts"] = adata.X.copy()
     adata.obs["cell_type"] = np.random.choice(["a", "b", "c"], adata.n_obs).tolist()
     adata.obs_names_make_unique()
@@ -18,8 +18,8 @@ def get_adata() -> sc.AnnData:
 
 def get_adata_2() -> sc.AnnData:
     adata = sc.datasets.visium_sge("V1_Breast_Cancer_Block_A_Section_2")
-    # random sample 600 cells
-    # adata = adata[np.random.choice(adata.obs.index, 600), :].copy()
+    # sample first 600 cells
+    adata = adata[:600, :]
     adata.layers["counts"] = adata.X.copy()
     adata.obs["cell_type"] = np.random.choice(["a", "b", "c"], adata.n_obs).tolist()
     adata.obs_names_make_unique()