Index: trunk/test/unit/org/openstreetmap/josm/data/projection/proj/AbstractProjTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/data/projection/proj/AbstractProjTest.java	(revision 18353)
+++ trunk/test/unit/org/openstreetmap/josm/data/projection/proj/AbstractProjTest.java	(revision 18353)
@@ -0,0 +1,45 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.data.projection.proj;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+import org.openstreetmap.josm.data.Bounds;
+
+/**
+ * Unit tests of {@link AbstractProj}
+ */
+class AbstractProjTest {
+
+    private final AbstractProj proj = new AbstractProj() {
+
+        @Override
+        public String getName() {
+            return null;
+        }
+
+        @Override
+        public String getProj4Id() {
+            return null;
+        }
+
+        @Override
+        public double[] project(double latRad, double lonRad) {
+            return null;
+        }
+
+        @Override
+        public double[] invproject(double east, double north) {
+            return null;
+        }
+
+        @Override
+        public Bounds getAlgorithmBounds() {
+            return null;
+        }};
+
+    @Test
+    void testCphi2NaN() {
+        assertTrue(Double.isNaN(proj.cphi2(Double.NaN)));
+    }
+}