1 files changed, 69 insertions, 0 deletions

diff --git a/test/models/helpers/revisions_helper_test.rb b/test/models/helpers/revisions_helper_test.rb
index 6bb5f077..f59823f9 100644
--- a/test/models/helpers/revisions_helper_test.rb
+++ b/test/models/helpers/revisions_helper_test.rb
@@ -1,4 +1,73 @@
 require 'test_helper'
 
 class RevisionsHelperTest < ActionView::TestCase
+  class RevisionSet
+    def initialize revisions
+      @revisions = revisions
+    end
+
+    def pages
+      self
+    end
+
+    def exists? conditions
+      @revisions.include?(conditions[:revision])
+    end
+  end
+
+  def node_with *revisions
+    RevisionSet.new(revisions)
+  end
+
+  test "a forward pair offers both neighbours in forward orientation" do
+    assert_equal [[2, 3], [4, 5]],
+                 neighbour_revision_pairs(node_with(1, 2, 3, 4, 5), 3, 4)
+  end
+
+  test "a reverse pair offers both neighbours in reverse orientation" do
+    assert_equal [[3, 2], [5, 4]],
+                 neighbour_revision_pairs(node_with(1, 2, 3, 4, 5), 4, 3)
+  end
+
+  test "the earliest pair has no earlier neighbour" do
+    assert_equal [nil, [2, 3]],
+                 neighbour_revision_pairs(node_with(1, 2, 3), 1, 2)
+  end
+
+  test "the latest pair has no later neighbour" do
+    assert_equal [[1, 2], nil],
+                 neighbour_revision_pairs(node_with(1, 2, 3), 2, 3)
+  end
+
+  test "a layer comparison offers no neighbours" do
+    assert_equal [nil, nil],
+                 neighbour_revision_pairs(node_with(1, 2, 3), "head", "draft")
+  end
+
+  test "mixing a layer with a number offers no neighbours" do
+    assert_equal [nil, nil],
+                 neighbour_revision_pairs(node_with(1, 2, 3), "head", 3)
+  end
+
+  test "a non-adjacent pair offers no neighbours" do
+    assert_equal [nil, nil],
+                 neighbour_revision_pairs(node_with(1, 2, 3, 4, 5), 2, 5)
+  end
+
+  # The controller sets both ends to 1 when a node has a single page.
+  test "a revision compared against itself offers no neighbours" do
+    assert_equal [nil, nil], neighbour_revision_pairs(node_with(1), 1, 1)
+  end
+
+  test "string references are accepted, since they arrive from the query string" do
+    assert_equal [[1, 2], nil],
+                 neighbour_revision_pairs(node_with(1, 2, 3), "2", "3")
+  end
+
+  # Revision numbers are contiguous today. Should that stop being true, the
+  # control disables rather than pointing at a revision that is not there.
+  test "a gap disables the control rather than skipping over it" do
+    assert_equal [nil, [5, 6]],
+                 neighbour_revision_pairs(node_with(1, 2, 4, 5, 6), 4, 5)
+  end
 end