diff --git a/src/mol-math/linear-algebra/_spec/principal-axes.spec.ts b/src/mol-math/linear-algebra/_spec/principal-axes.spec.ts
new file mode 100644
index 0000000000000000000000000000000000000000..13111e916b6045d0141c33c4edbe57621c62fb3f
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+++ b/src/mol-math/linear-algebra/_spec/principal-axes.spec.ts
@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) 2019 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ *
+ * @author Gianluca Tomasello <giagitom@gmail.com>
+ */
+
+import { NumberArray } from '../../../mol-util/type-helpers';
+import { PrincipalAxes } from '../matrix/principal-axes';
+
+describe('PrincipalAxes', () => {
+    it('same-cartesian-plane', () => {
+        const positions : NumberArray = [ //same y coordinate
+            0.1945, -0.0219, -0.0416,
+            -0.0219,-0.0219, -0.0119,
+        ];
+        const { origin, dirA, dirB, dirC } = PrincipalAxes.ofPositions(positions).boxAxes;
+        expect( origin[0] !== Infinity && origin[1] !== Infinity && origin[2] !== Infinity ).toBe(true);
+    });
+});