Raise ValueError when parameters specified incorrectly.

sympy/vector/parametricregion.py

@@ -23,6 +23,10 @@ def __new__(cls, *args, system=None):
             else:
                 definition.append(arg)
 
+        for bound in bounds:
+            if len(bound) != 3:
+                raise ValueError("Parameters should be specified in the form (paramteter, lower bound, upper bound)")
+
         for elem in bounds:
             parameters.append(elem[0])
 

sympy/vector/tests/test_parametricregion.py

@@ -0,0 +1,50 @@
+from sympy import sin, cos, pi, symbols
+from sympy.vector.coordsysrect import CoordSys3D
+from sympy.vector.parametricregion import ParametricRegion
+
+C = CoordSys3D('C')
+r, theta, phi, a, b, t = symbols('r theta phi a b t')
+
+def test_parametricregion():
+
+    point = ParametricRegion(3, 4)
+    assert point.definition == [3, 4]
+    assert point.parameters == []
+    assert point.bounds == []
+    assert point.system == None
+
+    l = ParametricRegion(C.y, (C.y, -3, 3), system=C)
+    assert l.definition == [C.y]
+    assert l.parameters == [C.y]
+    assert l.system == C
+
+    p1 = ParametricRegion(9*a, -16*b, (a, 0, 3))
+    assert p1.definition == [9*a, -16*b]
+    assert p1.parameters == [a]
+    assert p1.bounds == [(a, 0, 3)]
+
+    circle = ParametricRegion(r*cos(theta), r*sin(theta), (theta, 0, 2*pi))
+    assert circle.definition == [r*cos(theta), r*sin(theta)]
+    assert circle.system == None
+
+    halfdisc = ParametricRegion(r*cos(theta), r* sin(theta), (r, -2, 2), (theta, 0, pi))
+    assert halfdisc.definition == [r*cos(theta), r*sin(theta)]
+    assert halfdisc.parameters == [r, theta]
+    assert halfdisc.bounds == [(r, -2, 2), (theta, 0, pi)]
+
+    parabola = ParametricRegion(a*t**2, 2*a*t, (t, -2, 2))
+    assert parabola.definition == [a*t**2, 2*a*t]
+    assert parabola.parameters == [t]
+
+    ellipse = ParametricRegion(a*cos(t), b*sin(t), (t, 0, 8))
+    assert ellipse.parameters == [t]
+    assert ellipse.bounds == [(t, 0, 8)]
+
+    sphere = ParametricRegion(r*sin(phi)*cos(theta),r*sin(phi)*sin(theta), r*cos(phi), (theta, 0, 2*pi), (phi, 0, pi))
+    assert sphere.definition == [r*sin(phi)*cos(theta),r*sin(phi)*sin(theta), r*cos(phi)]
+    assert sphere.parameters == [theta, phi]
+    assert sphere.system == None
+
+    cylinder = ParametricRegion(r*cos(theta), r*sin(theta), C.z, (theta, 0, 2*pi), (C.z, 0, 4), system=C)
+    assert cylinder.parameters == [theta, C.z]
+    assert cylinder.system == C