Harden the Paginate constructor against missing/invalid config

lib/perron/paginate.rb

@@ -2,10 +2,14 @@
 
 module Perron
   class Paginate
-    def initialize(collection, page:, per_page:, base_path: nil, page_path_template: nil, use_query_params: false)
+    def initialize(collection, page:, per_page:, base_path: "/", page_path_template: nil, use_query_params: false)
+      unless per_page.is_a?(Integer) && per_page.positive?
+        raise ArgumentError, "per_page must be a positive integer, got #{per_page.inspect}"
+      end
+
       @collection = collection
       @per_page = per_page
-      @base_path = base_path
+      @base_path = base_path || "/"
       @page_path_template = page_path_template || "/page/:page/"
       @use_query_params = use_query_params
 

test/perron/paginate_test.rb

@@ -193,4 +193,32 @@ class Perron::PaginateTest < ActiveSupport::TestCase
 
     assert_equal "/articles/?page=2", paginate.previous
   end
+
+  test "next falls back to a root-relative path when base_path is omitted" do
+    paginate = Perron::Paginate.new((1..10).to_a, page: 1, per_page: 5)
+
+    assert_equal "/page/2/", paginate.next
+  end
+
+  test "previous falls back to root when base_path is omitted" do
+    paginate = Perron::Paginate.new((1..10).to_a, page: 2, per_page: 5)
+
+    assert_equal "/", paginate.previous
+  end
+
+  test "an explicit nil base_path is treated as root" do
+    paginate = Perron::Paginate.new((1..10).to_a, page: 1, per_page: 5, base_path: nil)
+
+    assert_equal "/page/2/", paginate.next
+  end
+
+  test "raises ArgumentError for a non-positive or non-integer per_page" do
+    [0, -5, nil, 2.5].each do |bad|
+      error = assert_raises(ArgumentError) do
+        Perron::Paginate.new((1..10).to_a, page: 1, per_page: bad)
+      end
+
+      assert_match(/per_page must be a positive integer/, error.message)
+    end
+  end
 end