diff --git a/backend/spec/requests/gekanator_learning_spec.rb b/backend/spec/requests/gekanator_learning_spec.rb
new file mode 100644
index 0000000..4d11522
--- /dev/null
+++ b/backend/spec/requests/gekanator_learning_spec.rb
@@ -0,0 +1,588 @@
+require 'rails_helper'
+
+RSpec.describe 'Gekanator learning API', type: :request do
+  let(:admin) { create(:user, :admin) }
+  let(:member) { create(:user, :member) }
+  let(:other_user) { create(:user, :member) }
+
+  let!(:guessed_post) do
+    Post.create!(
+      title: 'guessed',
+      url: 'https://example.com/guessed'
+    )
+  end
+
+  let!(:correct_post) do
+    Post.create!(
+      title: 'correct',
+      url: 'https://example.com/correct'
+    )
+  end
+
+  let!(:other_post) do
+    Post.create!(
+      title: 'other',
+      url: 'https://example.com/other'
+    )
+  end
+
+  let!(:game) do
+    GekanatorGame.create!(
+      user: admin,
+      guessed_post: guessed_post,
+      correct_post: correct_post,
+      won: false,
+      question_count: 1,
+      answers: [
+        {
+          'question_id' => 'tag:character:喜多郁代',
+          'question_text' => '喜多ちゃんが関係してる?',
+          'answer' => 'yes',
+          'original_answer' => 'yes'
+        }
+      ]
+    )
+  end
+
+  def create_post_similarity_question!(
+    text: '喜多ちゃんが泣いてる?',
+    post: correct_post,
+    answer: 'yes',
+    status: 'accepted',
+    source: 'user_suggested',
+    priority_weight: 1.2
+  )
+    GekanatorQuestion.create!(
+      text: text,
+      kind: 'post_similarity',
+      source: source,
+      status: status,
+      priority_weight: priority_weight,
+      condition: {
+        type: 'post-similarity',
+        postId: post.id,
+        answer: answer,
+        threshold: 0.65
+      },
+      created_by: admin
+    )
+  end
+
+  describe 'POST /gekanator/games' do
+    it 'stores a game result for an admin user' do
+      sign_in_as admin
+
+      post '/gekanator/games', params: {
+        guessed_post_id: guessed_post.id,
+        correct_post_id: correct_post.id,
+        answers: [
+          {
+            question_id: 'tag:character:喜多郁代',
+            question_text: '喜多ちゃんが関係してる?',
+            answer: 'yes',
+            original_answer: 'yes'
+          }
+        ]
+      }
+
+      expect(response).to have_http_status(:created)
+
+      created = GekanatorGame.find(json['id'])
+      expect(created.user).to eq(admin)
+      expect(created.guessed_post).to eq(guessed_post)
+      expect(created.correct_post).to eq(correct_post)
+      expect(created.won).to eq(false)
+      expect(created.question_count).to eq(1)
+      expect(created.answers).to eq([
+        {
+          'question_id' => 'tag:character:喜多郁代',
+          'question_text' => '喜多ちゃんが関係してる?',
+          'answer' => 'yes',
+          'original_answer' => 'yes'
+        }
+      ])
+    end
+
+    it 'stores a won game when guessed_post_id equals correct_post_id' do
+      sign_in_as admin
+
+      post '/gekanator/games', params: {
+        guessed_post_id: correct_post.id,
+        correct_post_id: correct_post.id,
+        answers: []
+      }
+
+      expect(response).to have_http_status(:created)
+      expect(GekanatorGame.find(json['id']).won).to eq(true)
+    end
+
+    it 'rejects a game without correct_post_id' do
+      sign_in_as admin
+
+      expect {
+        post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          answers: []
+        }
+      }.not_to change { GekanatorGame.count }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'returns not found for a non-admin user' do
+      sign_in_as member
+
+      post '/gekanator/games', params: {
+        guessed_post_id: guessed_post.id,
+        correct_post_id: correct_post.id,
+        answers: []
+      }
+
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  describe 'POST /gekanator/question_suggestions' do
+    it 'creates a suggestion and promotes yes answer to an accepted post_similarity question' do
+      sign_in_as admin
+
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: game.id,
+          question_text: '喜多ちゃんが泣いてる?',
+          answer: 'yes'
+        }
+      }.to change { GekanatorQuestionSuggestion.count }.by(1)
+        .and change { GekanatorQuestion.count }.by(1)
+        .and change { GekanatorQuestionExample.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+
+      suggestion = GekanatorQuestionSuggestion.last
+      question = GekanatorQuestion.last
+      example = GekanatorQuestionExample.last
+
+      expect(json).to include(
+        'id' => suggestion.id,
+        'count' => 1
+      )
+
+      expect(suggestion).to have_attributes(
+        gekanator_game_id: game.id,
+        user_id: admin.id,
+        question_text: '喜多ちゃんが泣いてる?',
+        answer: 'yes',
+        processed: true
+      )
+
+      expect(question).to have_attributes(
+        text: '喜多ちゃんが泣いてる?',
+        kind: 'post_similarity',
+        source: 'user_suggested',
+        status: 'accepted',
+        priority_weight: 1.2,
+        gekanator_question_suggestion_id: suggestion.id,
+        created_by_id: admin.id
+      )
+      expect(question.condition).to include(
+        'type' => 'post-similarity',
+        'postId' => correct_post.id,
+        'answer' => 'yes',
+        'threshold' => 0.65
+      )
+
+      expect(example).to have_attributes(
+        gekanator_question_id: question.id,
+        post_id: correct_post.id,
+        user_id: admin.id,
+        gekanator_game_id: game.id,
+        answer: 'yes',
+        source: 'initial_suggestion',
+        weight: 1.0
+      )
+    end
+
+    it 'promotes no, partial, and probably_no answers' do
+      sign_in_as admin
+
+      ['no', 'partial', 'probably_no'].each do |answer|
+        expect {
+          post '/gekanator/question_suggestions', params: {
+            gekanator_game_id: game.id,
+            question_text: "answer #{answer} question?",
+            answer: answer
+          }
+        }.to change { GekanatorQuestion.count }.by(1)
+          .and change { GekanatorQuestionExample.count }.by(1)
+
+        expect(response).to have_http_status(:created)
+        expect(GekanatorQuestion.last.condition['answer']).to eq(answer)
+        expect(GekanatorQuestionExample.last.answer).to eq(answer)
+      end
+    end
+
+    it 'does not promote unknown answers' do
+      sign_in_as admin
+
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: game.id,
+          question_text: 'よく分からない質問?',
+          answer: 'unknown'
+        }
+      }.to change { GekanatorQuestionSuggestion.count }.by(1)
+        .and change { GekanatorQuestion.count }.by(0)
+        .and change { GekanatorQuestionExample.count }.by(0)
+
+      expect(response).to have_http_status(:created)
+      expect(GekanatorQuestionSuggestion.last.processed).to eq(false)
+    end
+
+    it 'limits suggestions to three per game' do
+      sign_in_as admin
+
+      3.times do |i|
+        GekanatorQuestionSuggestion.create!(
+          gekanator_game: game,
+          user: admin,
+          question_text: "existing question #{i}",
+          answer: 'unknown'
+        )
+      end
+
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: game.id,
+          question_text: 'fourth question?',
+          answer: 'yes'
+        }
+      }.not_to change { GekanatorQuestionSuggestion.count }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'returns not found for a non-admin user' do
+      sign_in_as member
+
+      post '/gekanator/question_suggestions', params: {
+        gekanator_game_id: game.id,
+        question_text: 'member question?',
+        answer: 'yes'
+      }
+
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  describe 'GET /gekanator/games/:id/extra_questions' do
+    it 'returns at most two accepted user_suggested post_similarity questions' do
+      sign_in_as admin
+
+      low = create_post_similarity_question!(
+        text: 'low?',
+        priority_weight: 1.0
+      )
+      high = create_post_similarity_question!(
+        text: 'high?',
+        priority_weight: 3.0
+      )
+      middle = create_post_similarity_question!(
+        text: 'middle?',
+        priority_weight: 2.0
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].length).to eq(2)
+      expect(json['questions'].map { _1['id'] }).to eq([high.id, middle.id])
+      expect(json['questions'].map { _1['id'] }).not_to include(low.id)
+    end
+
+    it 'does not return questions that already have an example for the correct post' do
+      sign_in_as admin
+
+      existing = create_post_similarity_question!(text: 'already learned?')
+      fresh = create_post_similarity_question!(text: 'fresh?')
+
+      GekanatorQuestionExample.create!(
+        gekanator_question: existing,
+        post: correct_post,
+        user: admin,
+        gekanator_game: game,
+        answer: 'yes',
+        source: 'post_game_extra'
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to include(fresh.id)
+      expect(json['questions'].map { _1['id'] }).not_to include(existing.id)
+    end
+
+    it 'does not return questions already asked in the game using snake_case question_id' do
+      sign_in_as admin
+
+      asked = create_post_similarity_question!(text: 'already asked?')
+      fresh = create_post_similarity_question!(text: 'fresh?')
+      game.update!(
+        answers: [
+          {
+            'question_id' => "post-similarity:#{asked.id}",
+            'answer' => 'yes'
+          }
+        ]
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to include(fresh.id)
+      expect(json['questions'].map { _1['id'] }).not_to include(asked.id)
+    end
+
+    it 'does not return questions already asked in the game using camelCase questionId' do
+      sign_in_as admin
+
+      asked = create_post_similarity_question!(text: 'already asked?')
+      fresh = create_post_similarity_question!(text: 'fresh?')
+      game.update!(
+        answers: [
+          {
+            'questionId' => "post-similarity:#{asked.id}",
+            'answer' => 'yes'
+          }
+        ]
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to include(fresh.id)
+      expect(json['questions'].map { _1['id'] }).not_to include(asked.id)
+    end
+
+    it 'does not return non-accepted, non-user_suggested, or non-post_similarity questions' do
+      sign_in_as admin
+
+      accepted = create_post_similarity_question!(text: 'accepted?')
+      create_post_similarity_question!(text: 'disabled?', status: 'disabled')
+      create_post_similarity_question!(text: 'ai?', source: 'ai_generated')
+      GekanatorQuestion.create!(
+        text: 'tag?',
+        kind: 'tag',
+        source: 'user_suggested',
+        status: 'accepted',
+        priority_weight: 1.0,
+        condition: { type: 'tag', key: 'character:喜多郁代' }
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to contain_exactly(accepted.id)
+    end
+  end
+
+  describe 'POST /gekanator/games/:id/extra_question_answers' do
+    it 'creates examples for extra question answers' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(text: 'extra?')
+
+      expect {
+        post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+          answers: [
+            {
+              question_id: question.id.to_s,
+              answer: 'partial'
+            }
+          ]
+        }
+      }.to change { GekanatorQuestionExample.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+      expect(json).to include('count' => 1)
+
+      example = GekanatorQuestionExample.last
+      expect(example).to have_attributes(
+        gekanator_question_id: question.id,
+        post_id: correct_post.id,
+        user_id: admin.id,
+        gekanator_game_id: game.id,
+        answer: 'partial',
+        source: 'post_game_extra',
+        weight: 1.0
+      )
+    end
+
+    it 'updates an existing example for the same question, post, and user' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(text: 'extra?')
+      existing = GekanatorQuestionExample.create!(
+        gekanator_question: question,
+        post: correct_post,
+        user: admin,
+        answer: 'no',
+        source: 'post_game_extra',
+        weight: 1.0
+      )
+
+      expect {
+        post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+          answers: [
+            {
+              question_id: question.id,
+              answer: 'yes'
+            }
+          ]
+        }
+      }.not_to change { GekanatorQuestionExample.count }
+
+      expect(response).to have_http_status(:created)
+      expect(existing.reload).to have_attributes(
+        answer: 'yes',
+        source: 'post_game_extra',
+        gekanator_game_id: game.id
+      )
+    end
+
+    it 'rejects missing questions' do
+      sign_in_as admin
+
+      expect {
+        post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+          answers: [
+            {
+              question_id: 999_999_999,
+              answer: 'yes'
+            }
+          ]
+        }
+      }.not_to change { GekanatorQuestionExample.count }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'rejects non-accepted questions' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(
+        text: 'disabled?',
+        status: 'disabled'
+      )
+
+      post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+        answers: [
+          {
+            question_id: question.id,
+            answer: 'yes'
+          }
+        ]
+      }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'rejects non-post_similarity questions' do
+      sign_in_as admin
+
+      question = GekanatorQuestion.create!(
+        text: 'tag?',
+        kind: 'tag',
+        source: 'user_suggested',
+        status: 'accepted',
+        priority_weight: 1.0,
+        condition: { type: 'tag', key: 'character:喜多郁代' }
+      )
+
+      post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+        answers: [
+          {
+            question_id: question.id,
+            answer: 'yes'
+          }
+        ]
+      }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+  end
+
+  describe 'GET /gekanator/questions' do
+    it 'returns accepted questions only and includes example_answers for post_similarity questions' do
+      sign_in_as admin
+
+      accepted = create_post_similarity_question!(text: 'accepted?')
+      create_post_similarity_question!(
+        text: 'disabled?',
+        status: 'disabled'
+      )
+
+      GekanatorQuestionExample.create!(
+        gekanator_question: accepted,
+        post: correct_post,
+        user: admin,
+        answer: 'yes',
+        source: 'initial_suggestion',
+        weight: 1.0
+      )
+
+      get '/gekanator/questions'
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].length).to eq(1)
+
+      question_json = json['questions'].first
+      expect(question_json).to include(
+        'id' => "post-similarity:#{accepted.id}",
+        'text' => 'accepted?',
+        'kind' => 'post_similarity',
+        'source' => 'user_suggested',
+        'priority_weight' => 1.2
+      )
+      expect(question_json['condition']).to include(
+        'type' => 'post-similarity',
+        'postId' => correct_post.id,
+        'answer' => 'yes',
+        'threshold' => 0.65
+      )
+      expect(question_json['example_answers']).to include(
+        correct_post.id.to_s => 'yes'
+      )
+    end
+
+    it 'aggregates example_answers by weight' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(text: 'weighted?')
+
+      GekanatorQuestionExample.create!(
+        gekanator_question: question,
+        post: other_post,
+        user: admin,
+        answer: 'yes',
+        source: 'post_game_extra',
+        weight: 1.0
+      )
+      GekanatorQuestionExample.create!(
+        gekanator_question: question,
+        post: other_post,
+        user: other_user,
+        answer: 'no',
+        source: 'post_game_extra',
+        weight: 2.0
+      )
+
+      get '/gekanator/questions'
+
+      expect(response).to have_http_status(:ok)
+      question_json = json['questions'].find { _1['id'] == "post-similarity:#{question.id}" }
+      expect(question_json['example_answers']).to include(
+        other_post.id.to_s => 'no'
+      )
+    end
+  end
+end
diff --git a/frontend/src/lib/gekanator.test.ts b/frontend/src/lib/gekanator.test.ts
new file mode 100644
index 0000000..5afb8f7
--- /dev/null
+++ b/frontend/src/lib/gekanator.test.ts
@@ -0,0 +1,296 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { apiPost } from '@/lib/api'
+import {
+  expectedAnswerForQuestion,
+  restoreGekanatorQuestion,
+  saveGekanatorExtraQuestionAnswers,
+  saveGekanatorGame,
+  saveGekanatorQuestionSuggestion,
+} from '@/lib/gekanator'
+
+import type {
+  GekanatorAnswerLog,
+  StoredGekanatorQuestion,
+} from '@/lib/gekanator'
+import type { Post } from '@/types'
+
+vi.mock('@/lib/api', () => ({
+  apiGet: vi.fn(),
+  apiPost: vi.fn(),
+}))
+
+const mockedApiPost = vi.mocked(apiPost)
+
+const post = (overrides: Partial<Post> = {}): Post => ({
+  id: 1,
+  url: 'https://example.com/posts/1',
+  title: 'post title',
+  thumbnail: null,
+  thumbnailBase: null,
+  tags: [],
+  viewed: false,
+  related: [],
+  originalCreatedFrom: null,
+  originalCreatedBefore: null,
+  createdAt: '2026-06-10T00:00:00.000Z',
+  updatedAt: '2026-06-10T00:00:00.000Z',
+  uploadedUser: null,
+  ...overrides,
+})
+
+describe('expectedAnswerForQuestion', () => {
+  it('returns a direct example answer when present', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 999,
+        answer: 'yes',
+        threshold: 0.65,
+      },
+      exampleAnswers: {
+        1: 'partial',
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ id: 1 }))).toBe('partial')
+  })
+
+  it('returns the condition answer for the original post_similarity post', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 123,
+        answer: 'probably_no',
+        threshold: 0.65,
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ id: 123 }))).toBe('probably_no')
+  })
+
+  it('returns null for an unrelated post_similarity post without examples', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 123,
+        answer: 'yes',
+        threshold: 0.65,
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ id: 456 }))).toBeNull()
+  })
+
+  it('returns yes for a matching tag question', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'tag:character:喜多郁代',
+      text: '喜多ちゃんが関係してる?',
+      kind: 'tag',
+      condition: {
+        type: 'tag',
+        key: 'character:喜多郁代',
+      },
+    }
+
+    expect(
+      expectedAnswerForQuestion(
+        question,
+        post({
+          tags: [
+            {
+              id: 1,
+              name: '喜多郁代',
+              category: 'character',
+              aliases: [],
+              parents: [],
+              postCount: 1,
+              createdAt: '2026-06-10T00:00:00.000Z',
+              updatedAt: '2026-06-10T00:00:00.000Z',
+              hasWiki: false,
+              materialId: null,
+            },
+          ],
+        }),
+      ),
+    ).toBe('yes')
+  })
+
+  it('returns no for a non-matching tag question', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'tag:character:喜多郁代',
+      text: '喜多ちゃんが関係してる?',
+      kind: 'tag',
+      condition: {
+        type: 'tag',
+        key: 'character:喜多郁代',
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ tags: [] }))).toBe('no')
+  })
+})
+
+describe('restoreGekanatorQuestion', () => {
+  it('uses default source and priority weight when omitted', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'tag:character:喜多郁代',
+      text: '喜多ちゃんが関係してる?',
+      kind: 'tag',
+      condition: {
+        type: 'tag',
+        key: 'character:喜多郁代',
+      },
+    })
+
+    expect(question.source).toBe('default')
+    expect(question.priorityWeight).toBe(1)
+  })
+
+  it('tests a post_similarity question using direct examples', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 999,
+        answer: 'yes',
+        threshold: 0.65,
+      },
+      exampleAnswers: {
+        1: 'yes',
+        2: 'no',
+      },
+    })
+
+    expect(question.test(post({ id: 1 }))).toBe(true)
+    expect(question.test(post({ id: 2 }))).toBe(false)
+    expect(question.test(post({ id: 3 }))).toBe(false)
+  })
+})
+
+describe('Gekanator API writers', () => {
+  beforeEach(() => {
+    mockedApiPost.mockReset()
+  })
+
+  it('sends game results using snake_case request keys', async () => {
+    mockedApiPost.mockResolvedValue({ id: 100 })
+
+    const answers: GekanatorAnswerLog[] = [
+      {
+        questionId: 'tag:character:喜多郁代',
+        questionText: '喜多ちゃんが関係してる?',
+        questionCondition: {
+          type: 'tag',
+          key: 'character:喜多郁代',
+        },
+        answer: 'yes',
+        originalAnswer: 'partial',
+      },
+    ]
+
+    await expect(
+      saveGekanatorGame({
+        guessedPostId: 1,
+        correctPostId: 2,
+        answers,
+      }),
+    ).resolves.toEqual({ id: 100 })
+
+    expect(mockedApiPost).toHaveBeenCalledWith('/gekanator/games', {
+      guessed_post_id: 1,
+      correct_post_id: 2,
+      answers: [
+        {
+          question_id: 'tag:character:喜多郁代',
+          question_text: '喜多ちゃんが関係してる?',
+          question_condition: {
+            type: 'tag',
+            key: 'character:喜多郁代',
+          },
+          answer: 'yes',
+          original_answer: 'partial',
+        },
+      ],
+    })
+  })
+
+  it('sends question suggestions using snake_case request keys', async () => {
+    mockedApiPost.mockResolvedValue({
+      id: 10,
+      count: 1,
+    })
+
+    await expect(
+      saveGekanatorQuestionSuggestion({
+        gekanatorGameId: 100,
+        questionText: '喜多ちゃんが泣いてる?',
+        answer: 'yes',
+      }),
+    ).resolves.toEqual({
+      id: 10,
+      count: 1,
+    })
+
+    expect(mockedApiPost).toHaveBeenCalledWith('/gekanator/question_suggestions', {
+      gekanator_game_id: 100,
+      question_text: '喜多ちゃんが泣いてる?',
+      answer: 'yes',
+    })
+  })
+
+  it('sends extra question answers using snake_case request keys', async () => {
+    mockedApiPost.mockResolvedValue({
+      count: 2,
+    })
+
+    await saveGekanatorExtraQuestionAnswers({
+      gameId: 100,
+      answers: [
+        {
+          questionId: 10,
+          answer: 'yes',
+        },
+        {
+          questionId: 11,
+          answer: 'probably_no',
+        },
+      ],
+    })
+
+    expect(mockedApiPost).toHaveBeenCalledWith(
+      '/gekanator/games/100/extra_question_answers',
+      {
+        answers: [
+          {
+            question_id: 10,
+            answer: 'yes',
+          },
+          {
+            question_id: 11,
+            answer: 'probably_no',
+          },
+        ],
+      },
+    )
+  })
+})