diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 4de6df86..05d503fa 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -16,7 +16,7 @@ jobs:
         os: [ubuntu-latest, macos-latest]
         python-version: ['3.10', '3.11', '3.12', '3.13']
         mpi: ['mpich', 'openmpi', 'intelmpi']
-        rank: ['2', '3', '4']
+        rank: ['2', '4', '9']
         exclude:
           - os: macos-latest
             mpi: 'intelmpi'
@@ -43,4 +43,9 @@ jobs:
       - name: Install pylops-mpi
         run: pip install .
       - name: Testing using pytest-mpi
-        run: mpiexec -n ${{ matrix.rank }} pytest tests/ --with-mpi
+        run: |
+          if [ "${{ matrix.mpi }}" = "openmpi" ]; then
+            mpiexec --oversubscribe --mca btl ^openib --bind-to none -n ${{ matrix.rank }} pytest tests/ --with-mpi
+          else
+            mpiexec -n ${{ matrix.rank }} pytest tests/ --with-mpi
+          fi
diff --git a/Makefile b/Makefile
index 7d866764..d2715edd 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 PIP := $(shell command -v pip3 2> /dev/null || command which pip 2> /dev/null)
 PYTHON := $(shell command -v python3 2> /dev/null || command which python 2> /dev/null)
-NUM_PROCESSES = 3
+NUM_PROCESSES = 4
 
 .PHONY: install dev-install dev-install_nccl install_ \
 	conda install_conda_nccl dev-install_conda dev-install_conda_nccl  \
diff --git a/tests/test_distributedarray.py b/tests/test_distributedarray.py
index bc3d7a32..34944b06 100644
--- a/tests/test_distributedarray.py
+++ b/tests/test_distributedarray.py
@@ -199,12 +199,21 @@ def test_distributed_norm(par):
 def test_distributed_masked(par):
     """Test Asarray with masked array"""
     # Number of subcommunicators
-    if MPI.COMM_WORLD.Get_size() % 2 == 0:
+    size = MPI.COMM_WORLD.Get_size()
+    
+    # Exclude not handled cases
+    shape_axis = par['x'].shape[par['axis']]
+    print('shape_axis, size', shape_axis, size, shape_axis % size != 0)
+    if shape_axis % size != 0:
+        pytest.skip(f"Array dimension to distributed ({shape_axis}) is not  "
+                    f"divisible by the number of processes ({size})...")
+    if size % 2 == 0:
         nsub = 2
-    elif MPI.COMM_WORLD.Get_size() % 3 == 0:
+    elif size % 3 == 0:
         nsub = 3
     else:
-        pass
+        pytest.skip(f"Number of processes ({size}) is not divisible "
+                    "by 2 or 3...")
     subsize = max(1, MPI.COMM_WORLD.Get_size() // nsub)
     mask = np.repeat(np.arange(nsub), subsize)
 
@@ -236,12 +245,21 @@ def test_distributed_masked(par):
 def test_distributed_maskeddot(par1, par2):
     """Test Distributed Dot product with masked array"""
     # Number of subcommunicators
-    if MPI.COMM_WORLD.Get_size() % 2 == 0:
+    size = MPI.COMM_WORLD.Get_size()
+    
+    # Exclude not handled cases
+    shape_axis = par1['x'].shape[par1['axis']]
+    print('shape_axis, size', shape_axis, size, shape_axis % size != 0)
+    if shape_axis % size != 0:
+        pytest.skip(f"Array dimension to distributed ({shape_axis}) is not  "
+                    f"divisible by the number of processes ({size})...")
+    if size % 2 == 0:
         nsub = 2
-    elif MPI.COMM_WORLD.Get_size() % 3 == 0:
+    elif size % 3 == 0:
         nsub = 3
     else:
-        pass
+        pytest.skip(f"Number of processes ({size}) is not divisible "
+                    "by 2 or 3...")
     subsize = max(1, MPI.COMM_WORLD.Get_size() // nsub)
     mask = np.repeat(np.arange(nsub), subsize)
 
@@ -271,12 +289,21 @@ def test_distributed_maskeddot(par1, par2):
 def test_distributed_maskednorm(par):
     """Test Distributed numpy.linalg.norm method with masked array"""
     # Number of subcommunicators
-    if MPI.COMM_WORLD.Get_size() % 2 == 0:
+    size = MPI.COMM_WORLD.Get_size()
+
+    # Exclude not handled cases
+    shape_axis = par['x'].shape[par['axis']]
+    print('shape_axis, size', shape_axis, size, shape_axis % size != 0)
+    if shape_axis % size != 0:
+        pytest.skip(f"Array dimension to distributed ({shape_axis}) is not  "
+                    f"divisible by the number of processes ({size})...")
+    if size % 2 == 0:
         nsub = 2
-    elif MPI.COMM_WORLD.Get_size() % 3 == 0:
+    elif size % 3 == 0:
         nsub = 3
     else:
-        pass
+        pytest.skip(f"Number of processes ({size}) is not divisible "
+                    "by 2 or 3...")
     subsize = max(1, MPI.COMM_WORLD.Get_size() // nsub)
     mask = np.repeat(np.arange(nsub), subsize)
     # Replicate x as required in masked arrays
diff --git a/tests/test_fredholm.py b/tests/test_fredholm.py
index 3d45a4c6..95bd5468 100644
--- a/tests/test_fredholm.py
+++ b/tests/test_fredholm.py
@@ -20,7 +20,7 @@
 size = MPI.COMM_WORLD.Get_size()
 
 par1 = {
-    "nsl": 12,
+    "nsl": 21,
     "ny": 6,
     "nx": 4,
     "nz": 5,
@@ -30,7 +30,7 @@
     "dtype": "float32",
 }  # real, saved Gt
 par2 = {
-    "nsl": 12,
+    "nsl": 21,
     "ny": 6,
     "nx": 4,
     "nz": 5,
@@ -40,7 +40,7 @@
     "dtype": "float32",
 }  # real, unsaved Gt
 par3 = {
-    "nsl": 12,
+    "nsl": 21,
     "ny": 6,
     "nx": 4,
     "nz": 5,
@@ -50,7 +50,7 @@
     "dtype": "complex64",
 }  # complex, saved Gt
 par4 = {
-    "nsl": 12,
+    "nsl": 21,
     "ny": 6,
     "nx": 4,
     "nz": 5,
@@ -60,7 +60,7 @@
     "dtype": "complex64",
 }  # complex, unsaved Gt
 par5 = {
-    "nsl": 12,
+    "nsl": 21,
     "ny": 6,
     "nx": 4,
     "nz": 1,
@@ -70,7 +70,7 @@
     "dtype": "float32",
 }  # real, saved Gt, nz=1
 par6 = {
-    "nsl": 12,
+    "nsl": 21,
     "ny": 6,
     "nx": 4,
     "nz": 1,
diff --git a/tests/test_solver.py b/tests/test_solver.py
index 46e9a139..f79e3e61 100644
--- a/tests/test_solver.py
+++ b/tests/test_solver.py
@@ -26,7 +26,6 @@
     StackedDistributedArray
 )
 
-np.random.seed(42)
 size = MPI.COMM_WORLD.Get_size()
 rank = MPI.COMM_WORLD.Get_rank()
 
@@ -94,6 +93,8 @@
 )
 def test_cg(par):
     """CG with MPIBlockDiag"""
+    np.random.seed(42)
+    
     A = np.ones((par["ny"], par["nx"])) + par[
         "imag"] * np.ones((par["ny"], par["nx"]))
     Aop = MatrixMult(np.conj(A.T) @ A, dtype=par['dtype'])
@@ -139,6 +140,8 @@ def test_cg(par):
 )
 def test_cgls(par):
     """CGLS with MPIBlockDiag"""
+    np.random.seed(42)
+
     A = np.ones((par["ny"], par["nx"])) + par[
         "imag"] * np.ones((par["ny"], par["nx"]))
     Aop = MatrixMult(np.conj(A.T) @ A + 1e-5 * np.eye(par["nx"], dtype=par['dtype']),
@@ -186,6 +189,8 @@ def test_cgls(par):
 )
 def test_cgls_broadcastdata(par):
     """CGLS with broadcasted data vector"""
+    np.random.seed(42)
+
     A = (rank + 1) * np.ones((par["ny"], par["nx"])) + (rank + 2) * par[
         "imag"
     ] * np.ones((par["ny"], par["nx"]))
@@ -232,6 +237,8 @@ def test_cgls_broadcastdata(par):
 )
 def test_cgls_broadcastmodel(par):
     """CGLS with broadcasted model vector"""
+    np.random.seed(42)
+
     A = np.ones((par["ny"], par["nx"])) + par[
         "imag"] * np.ones((par["ny"], par["nx"]))
     Aop = MatrixMult(np.conj(A.T) @ A + 1e-5 * np.eye(par["nx"], dtype=par['dtype']),
@@ -281,6 +288,8 @@ def test_cgls_broadcastmodel(par):
 )
 def test_cg_stacked(par):
     """CG with MPIStackedBlockDiag"""
+    np.random.seed(42)
+
     A = np.ones((par["ny"], par["nx"])) + par[
         "imag"] * np.ones((par["ny"], par["nx"]))
     Aop = MatrixMult(np.conj(A.T) @ A + 1e-5 * np.eye(par["nx"], dtype=par['dtype']),
@@ -344,6 +353,8 @@ def test_cg_stacked(par):
 )
 def test_cgls_stacked(par):
     """CGLS with MPIStackedBlockDiag"""
+    np.random.seed(42)
+
     A = np.ones((par["ny"], par["nx"])) + par[
         "imag"] * np.ones((par["ny"], par["nx"]))
     Aop = MatrixMult(np.conj(A.T) @ A + 1e-5 * np.eye(par["nx"], dtype=par['dtype']),