Generate unique items for arrays with the "uniqueItems" property

CHANGELOG.md

@@ -1,3 +1,7 @@
+# 4.3.0
+
+* Generate unique items for arrays with the "uniqueItems" property. ([#63](https://github.com/alphagov/govuk_schemas/pull/63))
+
 # 4.2.0
 
 * Add support for generating random HH:MM time strings that match a regex. ([#62](https://github.com/alphagov/govuk_schemas/pull/62))

lib/govuk_schemas/random_schema_generator.rb

@@ -116,12 +116,27 @@ def generate_random_object(subschema)
     def generate_random_array(props)
       min = props["minItems"] || 0
       max = props["maxItems"] || 10
+      unique = props["uniqueItems"] == true
       num_items = @random.rand(min..max)
+      items = []
+      attempts = 0
+      max_attempts = num_items * 100
 
-      num_items.times.map do
+      until items.length == num_items
         # sometimes arrays don't have `items` specified, not sure if this is a bug
-        generate_value(props["items"] || {})
+        new_value = generate_value(props["items"] || {})
+
+        if unique && items.include?(new_value)
+          attempts += 1
+          raise "Failed to create a unique array item after #{max_attempts} attempts" if attempts >= max_attempts
+          next
+        end
+
+        attempts = 0
+        items << new_value
       end
+
+      items
     end
 
     def generate_random_string(props)

lib/govuk_schemas/version.rb

@@ -1,4 +1,4 @@
 module GovukSchemas
   # @private
-  VERSION = "4.2.0".freeze
+  VERSION = "4.3.0".freeze
 end

spec/lib/random_schema_generator_spec.rb

@@ -110,5 +110,44 @@
       expect(generator.payload["my_enum"]).to eq("a")
       expect(generator.payload.keys).to include("my_field")
     end
+
+    describe "unique arrays" do
+      it "handles arrays that require unique items" do
+        schema = {
+          "type" => "array",
+          "items" => { "type" => "string" },
+          "uniqueItems" => true,
+          "minItems" => 5,
+          "maxItems" => 5,
+        }
+
+        generator = GovukSchemas::RandomSchemaGenerator.new(schema: schema)
+
+        # These stubs are to ensure determinism in the random array value
+        # generation.
+        allow(generator).to receive(:generate_value).and_call_original
+        allow(generator)
+          .to receive(:generate_value)
+          .with({ "type" => "string" })
+          .and_return(*%w[a a b b c c d d e e])
+
+        expect(generator.payload).to match_array(%w[a b c d e])
+      end
+
+      it "raises an error for a situation where it can't generate a random array" do
+        schema = {
+          "type" => "array",
+          "items" => { "enum" => %w[a b] },
+          "uniqueItems" => true,
+          "minItems" => 3,
+          "maxItems" => 3,
+        }
+
+        generator = GovukSchemas::RandomSchemaGenerator.new(schema: schema)
+
+        expect { generator.payload }
+          .to raise_error "Failed to create a unique array item after 300 attempts"
+      end
+    end
   end
 end