Add spec for contributor coupling

lib/mosaik/extractors/evolution.rb

@@ -83,12 +83,18 @@ def call
         contributors.keys.permutation(2).each do |(a, b)|
           next if contributors[a].empty? || contributors[b].empty?
 
+          # Calculate coupling (cardinality of the intersection of sets of developers)
+          coupling = (contributors[a] & contributors[b]).count
+
+          # Skip if the coupling is one (no shared contributors)
+          next if coupling == 1
+
           graph.find_or_add_vertex(a)
           graph.find_or_add_vertex(b)
 
-          # Add a weighted edge to the graph (weight is the cardinality of the intersection of sets)
+          # Add a weighted edge to the graph
           # FIXME: aggregate with existing edges
-          graph.add_directed_edge(a, b, weight: (contributors[a] & contributors[b]).count * options[:contributor])
+          graph.add_directed_edge(a, b, weight: coupling * options[:contributor])
         end
       end
 

spec/mosaik/extractors/evolution_spec.rb

@@ -40,9 +40,26 @@
       expect(graph.vertices.transform_values { |v| v.edges.transform_values { |es| es.map { |e| e.attributes[:weight] } } }).to eq(
         "App::Foo" => { "App::Bak" => [1], "App::Bat" => [1], "App::Bar" => [1] },
         "App::Bar" => { "App::Foo" => [1] },
-        "App::Bat" => { "App::Baz" => [2], "App::Foo" => [1] },
+        "App::Bat" => { "App::Baz" => [3], "App::Foo" => [1] },
         "App::Bak" => { "App::Foo" => [1] },
-        "App::Baz" => { "App::Bat" => [2] },
+        "App::Baz" => { "App::Bat" => [3] },
+      )
+    end
+  end
+
+  describe "contributor coupling" do
+    let(:options) { { directory:, limit: 100, logical: 0, contributor: 1 } }
+
+    include_context "with a git repository"
+
+    it "constructs a contributor coupling graph" do
+      extractor.call
+
+      # Extract all vertices with source and destination
+      expect(graph.vertices.transform_values { |v| v.edges.transform_values { |es| es.map { |e| e.attributes[:weight] } } }).to eq(
+        "App::Foo" => { "App::Baz" => [2], "App::Bat" => [2] },
+        "App::Bat" => { "App::Baz" => [3], "App::Foo" => [2] },
+        "App::Baz" => { "App::Bat" => [3], "App::Foo" => [2] },
       )
     end
   end

spec/support/shared_contexts/repository.rb

@@ -8,6 +8,7 @@
 
   let(:john) { "John Doe <john@example.com>" }
   let(:jane) { "Jane Doe <jane@example.com>" }
+  let(:joey) { "Joey Doe <joey@example.com>" }
 
   def commit(author, **files_with_content)
     # Write the files with content
@@ -59,6 +60,10 @@ def commit(author, **files_with_content)
            "lib/app/bat.rb" => "class App::Bat; end",
            "lib/app/baz.rb" => "class App::Baz; def initialize; end; end"
 
+    commit joey,
+           "lib/app/bat.rb" => "class App::Bat; def initialize; end; end",
+           "lib/app/baz.rb" => "class App::Baz; end"
+
     # Mock the configuration
     allow(MOSAIK)
       .to receive(:configuration)