diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 04c66cc6..e73eb111 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -34,20 +34,20 @@ jobs:
     - name: Test package
       run: python -m pytest -ra
 
-  # root:
-  #   runs-on: ubuntu-latest
-  #   steps:
-  #   - uses: actions/checkout@v2
+  root:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
 
-  #   - name: Get Conda
-  #     uses: conda-incubator/setup-miniconda@v2
-  #     with:
-  #       environment-file: environment.yml
-  #       activate-environment: vector
+    - name: Get Conda
+      uses: conda-incubator/setup-miniconda@v2
+      with:
+        environment-file: environment.yml
+        activate-environment: vector
 
-  #   - name: Run tests
-  #     shell: "bash -l {0}"
-  #     run: python -m pytest tests/root_tests -ra
+    - name: Run tests
+      shell: "bash -l {0}"
+      run: python -m pytest tests/root -ra
 
   dist:
     runs-on: ubuntu-20.04
diff --git a/tests/root/test_PxPyPzEVector.py b/tests/root/test_PxPyPzEVector.py
new file mode 100644
index 00000000..2ba0491c
--- /dev/null
+++ b/tests/root/test_PxPyPzEVector.py
@@ -0,0 +1,64 @@
+# Copyright (c) 2019-2021, Jonas Eschle, Jim Pivarski, Eduardo Rodrigues, and Henry Schreiner.
+#
+# Distributed under the 3-clause BSD license, see accompanying file LICENSE
+# or https://github.com/scikit-hep/vector for details.
+
+import pytest
+
+import vector
+
+# If ROOT is not available, skip these tests.
+ROOT = pytest.importorskip("ROOT")
+
+# ROOT.Math.PxPyPzEVector constructor arguments to get all the weird cases.
+constructor = [
+    (0, 0, 0, 0),
+    (0, 0, 0, 10),
+    (0, 0, 0, -10),
+    (1, 2, 3, 0),
+    (1, 2, 3, 10),
+    (1, 2, 3, -10),
+    (1, 2, 3, 2.5),
+    (1, 2, 3, -2.5),
+]
+
+# Coordinate conversion methods to apply to the VectorObject4D.
+coordinates = [
+    "to_xyzt",
+    "to_xythetat",
+    "to_xyetat",
+    "to_rhophizt",
+    "to_rhophithetat",
+    "to_rhophietat",
+    "to_xyztau",
+    "to_xythetatau",
+    "to_xyetatau",
+    "to_rhophiztau",
+    "to_rhophithetatau",
+    "to_rhophietatau",
+]
+
+
+# Run a test that compares ROOT's 'M2()' with vector's 'tau2' for all cases.
+@pytest.mark.parametrize("constructor", constructor)
+@pytest.mark.parametrize("coordinates", coordinates)
+def test_M2(constructor, coordinates):
+    assert ROOT.Math.PxPyPzEVector(*constructor).M2() == pytest.approx(
+        getattr(
+            vector.obj(**dict(zip(["x", "y", "z", "t"], constructor))), coordinates
+        )().tau2
+    )
+
+
+# Run a test that compares ROOT's 'M()' with vector's 'tau' for all cases.
+@pytest.mark.parametrize("constructor", constructor)
+@pytest.mark.parametrize("coordinates", coordinates)
+def test_M(constructor, coordinates):
+    assert ROOT.Math.PxPyPzEVector(*constructor).M() == pytest.approx(
+        getattr(
+            vector.obj(**dict(zip(["x", "y", "z", "t"], constructor))), coordinates
+        )().tau
+    )
+
+
+# etc.