add org.scalacheck.Arbitrary instances for core geometric types

build.sbt

@@ -34,7 +34,6 @@ lazy val cell = defineModule("cell")(project)
   .dependsOn(numeric)
 
 lazy val geometry = defineModule("geometry")(project)
-  .dependsOn(testing % Test)
 
 lazy val io = defineModule("io")(project)
   .dependsOn(geometry, syntax)
@@ -65,7 +64,7 @@ lazy val pan = defineModule("pan")(project)
 lazy val syntax = defineModule("syntax")(project)
 
 lazy val testing = defineModule("testing", false)(project)
-  .dependsOn(imaging, numeric)
+  .dependsOn(geometry, imaging, numeric)
   .settings(libraryDependencies ++= Seq(
     scalacheck, 
     ironScalacheck,

modules/testing/src/main/scala/GeometricInstances.scala

@@ -0,0 +1,19 @@
+package at.ac.oeaw.imba.gerlich.gerlib.testing
+
+import cats.syntax.all.*
+import org.scalacheck.*
+
+import at.ac.oeaw.imba.gerlich.gerlib.geometry.*
+
+trait GeometricInstances extends CatsScalacheckInstances:
+    given arbitraryForXCoordinate[C](using c: Arbitrary[C]): Arbitrary[XCoordinate[C]] = c.fmap(XCoordinate.apply)
+
+    given arbitraryForYCoordinate[C](using c: Arbitrary[C]): Arbitrary[YCoordinate[C]] = c.fmap(YCoordinate.apply)
+
+    given arbitraryForZCoordinate[C](using c: Arbitrary[C]): Arbitrary[ZCoordinate[C]] = c.fmap(ZCoordinate.apply)
+
+    given arbitraryForPoint3D[C](using 
+        x: Arbitrary[XCoordinate[C]],
+        y: Arbitrary[YCoordinate[C]],
+        z: Arbitrary[ZCoordinate[C]],
+    ): Arbitrary[Point3D[C]] = (x, y, z).mapN(Point3D.apply)