From 33180c9f55df85dd302091c0bc924b01e995b79f Mon Sep 17 00:00:00 2001
From: Kevin Dew <kevindew@me.com>
Date: Mon, 8 Mar 2021 13:57:37 +0000
Subject: [PATCH 1/2] Generate unique items for arrays with the "uniqueItems"
 property

This re-calculates the values of an array if the "uniqueItems" property
is set and a non-unique item has been generated. This has been to help
resolve flaky tests that expect a random array and occasionally fail due
to the generation of an array with collisions.

As there is a risk that this can produce an eternal loop I've put in a
check that if there are very number of attempts to generate the unique
value then it should abort. This does produce a risk of failure if there
is a low amount of variance in the allowed variables.

This is to resolve issues such as:

```
GovukSchemas::InvalidContentGenerated: An invalid content item was generated.

This probably means there's a bug in the generator that causes it to output
invalid values. Below you'll find the generated payload, the validation errors
and the schema that was used.

...

Validation errors:
--------------------------

[
  {
    "schema": "869a7d30-f94e-5044-84e7-dc3c01c8f1ba#",
    "fragment": "#/details/featured_attachments",
    "message": "The property '#/details/featured_attachments' contained duplicated array values in schema 869a7d30-f94e-5044-84e7-dc3c01c8f1ba#",
    "failed_attribute": "UniqueItems"
  },
  {
    "schema": "869a7d30-f94e-5044-84e7-dc3c01c8f1ba",
    "fragment": "#/details/featured_attachments",
    "message": "The property '#/details/featured_attachments' contained duplicated array values in schema 869a7d30-f94e-5044-84e7-dc3c01c8f1ba",
    "failed_attribute": "UniqueItems"
  }
]
```
---
 lib/govuk_schemas/random_schema_generator.rb | 19 +++++++++-
 spec/lib/random_schema_generator_spec.rb     | 39 ++++++++++++++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/lib/govuk_schemas/random_schema_generator.rb b/lib/govuk_schemas/random_schema_generator.rb
index 0b6381d..6251a4f 100644
--- a/lib/govuk_schemas/random_schema_generator.rb
+++ b/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)
diff --git a/spec/lib/random_schema_generator_spec.rb b/spec/lib/random_schema_generator_spec.rb
index 82f0c98..6ff3f45 100644
--- a/spec/lib/random_schema_generator_spec.rb
+++ b/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

From 0d4216707a8c8aaa913765d08896bfa7b553997a Mon Sep 17 00:00:00 2001
From: Kevin Dew <kevindew@me.com>
Date: Mon, 8 Mar 2021 14:33:26 +0000
Subject: [PATCH 2/2] Bump version to 4.3.0

---
 CHANGELOG.md                 | 4 ++++
 lib/govuk_schemas/version.rb | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 497adfc..199a0ea 100644
--- a/CHANGELOG.md
+++ b/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))
diff --git a/lib/govuk_schemas/version.rb b/lib/govuk_schemas/version.rb
index 22ce071..f4df86a 100644
--- a/lib/govuk_schemas/version.rb
+++ b/lib/govuk_schemas/version.rb
@@ -1,4 +1,4 @@
 module GovukSchemas
   # @private
-  VERSION = "4.2.0".freeze
+  VERSION = "4.3.0".freeze
 end