Enhance test of range class for 100% code coverage

tests/range.be

@@ -23,3 +23,97 @@ assert(l == [])
 l = []
 for i:range(30, 0, -3) l..i end
 assert(l == [30, 27, 24, 21, 18, 15, 12, 9, 6, 3, 0])
+
+# lower(), upper(), incr() accessors
+var r = range(3, 7)
+assert(r.lower() == 3)
+assert(r.upper() == 7)
+assert(r.incr() == 1)
+
+var r2 = range(0, 20, 5)
+assert(r2.lower() == 0)
+assert(r2.upper() == 20)
+assert(r2.incr() == 5)
+
+var r3 = range(10, 0, -2)
+assert(r3.lower() == 10)
+assert(r3.upper() == 0)
+assert(r3.incr() == -2)
+
+# tostring - incr == 1 uses "(lower..upper)" format
+assert(str(range(1, 5)) == "(1..5)")
+
+# tostring - incr != 1 uses "range(lower, upper, incr)" format
+assert(str(range(0, 10, 3)) == "range(0, 10, 3)")
+assert(str(range(10, 0, -1)) == "range(10, 0, -1)")
+
+# setrange - basic usage
+var r4 = range(1, 5)
+r4.setrange(10, 20)
+assert(r4.lower() == 10)
+assert(r4.upper() == 20)
+assert(r4.incr() == 1)
+
+# setrange - with custom increment
+r4.setrange(0, 100, 10)
+assert(r4.lower() == 0)
+assert(r4.upper() == 100)
+assert(r4.incr() == 10)
+
+# setrange - verify iteration after setrange
+l = []
+var r5 = range(1, 3)
+r5.setrange(5, 9, 2)
+for i:r5 l..i end
+assert(l == [5, 7, 9])
+
+# init error: missing arguments
+try
+    range(1)
+    assert(false, "should raise")
+except .. as e, m
+    assert(e == 'value_error')
+end
+
+# init error: non-int arguments
+try
+    range(1, 2.0)
+    assert(false, "should raise")
+except .. as e, m
+    assert(e == 'value_error')
+end
+
+# init error: zero increment
+try
+    range(1, 10, 0)
+    assert(false, "should raise")
+except .. as e, m
+    assert(e == 'value_error')
+end
+
+# setrange error: missing arguments
+try
+    var r6 = range(1, 5)
+    r6.setrange(1)
+    assert(false, "should raise")
+except .. as e, m
+    assert(e == 'value_error')
+end
+
+# setrange error: non-int arguments
+try
+    var r7 = range(1, 5)
+    r7.setrange(1, "bad")
+    assert(false, "should raise")
+except .. as e, m
+    assert(e == 'value_error')
+end
+
+# setrange error: zero increment
+try
+    var r8 = range(1, 5)
+    r8.setrange(1, 10, 0)
+    assert(false, "should raise")
+except .. as e, m
+    assert(e == 'value_error')
+end