Allow setting of issue assignees in GraphQL

Adds GraphQL mutation to set issue assignees same as for merge requests.

app/graphql/mutations/concerns/mutations/assignable.rb

+# frozen_string_literal: true
+
+module Mutations
+  module Assignable
+    extend ActiveSupport::Concern
+
+    included do
+      argument :assignee_usernames,
+               [GraphQL::STRING_TYPE],
+               required: true,
+               description: 'The usernames to assign to the resource. Replaces existing assignees by default.'
+
+      argument :operation_mode,
+               Types::MutationOperationModeEnum,
+               required: false,
+               description: 'The operation to perform. Defaults to REPLACE.'
+    end
+
+    def resolve(project_path:, iid:, assignee_usernames:, operation_mode: Types::MutationOperationModeEnum.enum[:replace])
+      resource = authorized_find!(project_path: project_path, iid: iid)
+
+      Gitlab::QueryLimiting.whitelist('https://gitlab.com/gitlab-org/gitlab/issues/36098') if resource.is_a?(MergeRequest)
+
+      update_service_class.new(
+        resource.project,
+        current_user,
+        assignee_ids: assignee_ids(resource, assignee_usernames, operation_mode)
+      ).execute(resource)
+
+      {
+        resource.class.name.underscore.to_sym => resource,
+        errors: errors_on_object(resource)
+      }
+    end
+
+    private
+
+    def assignee_ids(resource, usernames, operation_mode)
+      assignee_ids = []
+      assignee_ids += resource.assignees.map(&:id) if Types::MutationOperationModeEnum.enum.values_at(:remove, :append).include?(operation_mode)
+      user_ids = UsersFinder.new(current_user, username: usernames).execute.map(&:id)
+
+      if operation_mode == Types::MutationOperationModeEnum.enum[:remove]
+        assignee_ids -= user_ids
+      else
+        assignee_ids |= user_ids
+      end
+
+      assignee_ids
+    end
+  end
+end

app/graphql/mutations/issues/set_assignees.rb

+# frozen_string_literal: true
+
+module Mutations
+  module Issues
+    class SetAssignees < Base
+      graphql_name 'IssueSetAssignees'
+
+      include Assignable
+
+      def update_service_class
+        ::Issues::UpdateService
+      end
+    end
+  end
+end

app/graphql/mutations/merge_requests/set_assignees.rb

@@ -5,43 +5,10 @@ module Mutations
     class SetAssignees < Base
       graphql_name 'MergeRequestSetAssignees'
 
-      argument :assignee_usernames,
-               [GraphQL::STRING_TYPE],
-               required: true,
-               description: <<~DESC
-                            The usernames to assign to the merge request. Replaces existing assignees by default.
-               DESC
+      include Assignable
 
-      argument :operation_mode,
-               Types::MutationOperationModeEnum,
-               required: false,
-               description: <<~DESC
-                            The operation to perform. Defaults to REPLACE.
-               DESC
-
-      def resolve(project_path:, iid:, assignee_usernames:, operation_mode: Types::MutationOperationModeEnum.enum[:replace])
-        Gitlab::QueryLimiting.whitelist('https://gitlab.com/gitlab-org/gitlab/issues/36098')
-
-        merge_request = authorized_find!(project_path: project_path, iid: iid)
-        project = merge_request.project
-
-        assignee_ids = []
-        assignee_ids += merge_request.assignees.map(&:id) if Types::MutationOperationModeEnum.enum.values_at(:remove, :append).include?(operation_mode)
-        user_ids = UsersFinder.new(current_user, username: assignee_usernames).execute.map(&:id)
-
-        if operation_mode == Types::MutationOperationModeEnum.enum[:remove]
-          assignee_ids -= user_ids
-        else
-          assignee_ids |= user_ids
-        end
-
-        ::MergeRequests::UpdateService.new(project, current_user, assignee_ids: assignee_ids)
-          .execute(merge_request)
-
-        {
-          merge_request: merge_request,
-          errors: errors_on_object(merge_request)
-        }
+      def update_service_class
+        ::MergeRequests::UpdateService
       end
     end
   end

app/graphql/types/mutation_type.rb

@@ -17,6 +17,7 @@ module Types
     mount_mutation Mutations::Branches::Create, calls_gitaly: true
     mount_mutation Mutations::Commits::Create, calls_gitaly: true
     mount_mutation Mutations::Discussions::ToggleResolve
+    mount_mutation Mutations::Issues::SetAssignees
     mount_mutation Mutations::Issues::SetConfidential
     mount_mutation Mutations::Issues::SetLocked
     mount_mutation Mutations::Issues::SetDueDate

changelogs/unreleased/graphql-issue-assignee.yml

+---
+title: Allow assign/unassign users to issues in GraphQL API.
+merge_request: 38081
+author:
+type: added

doc/api/graphql/reference/gitlab_schema.graphql

@@ -6269,6 +6269,56 @@ type IssuePermissions {
   updateIssue: Boolean!
 }
 
+"""
+Autogenerated input type of IssueSetAssignees
+"""
+input IssueSetAssigneesInput {
+  """
+  The usernames to assign to the resource. Replaces existing assignees by default.
+  """
+  assigneeUsernames: [String!]!
+
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  The IID of the issue to mutate
+  """
+  iid: String!
+
+  """
+  The operation to perform. Defaults to REPLACE.
+  """
+  operationMode: MutationOperationMode
+
+  """
+  The project the issue to mutate is in
+  """
+  projectPath: ID!
+}
+
+"""
+Autogenerated return type of IssueSetAssignees
+"""
+type IssueSetAssigneesPayload {
+  """
+  A unique identifier for the client performing the mutation.
+  """
+  clientMutationId: String
+
+  """
+  Errors encountered during execution of the mutation.
+  """
+  errors: [String!]!
+
+  """
+  The issue after mutation
+  """
+  issue: Issue
+}
+
 """
 Autogenerated input type of IssueSetConfidential
 """
@@ -7770,7 +7820,7 @@ Autogenerated input type of MergeRequestSetAssignees
 """
 input MergeRequestSetAssigneesInput {
   """
-  The usernames to assign to the merge request. Replaces existing assignees by default.
+  The usernames to assign to the resource. Replaces existing assignees by default.
   """
   assigneeUsernames: [String!]!
 
@@ -8410,6 +8460,7 @@ type Mutation {
   epicAddIssue(input: EpicAddIssueInput!): EpicAddIssuePayload
   epicSetSubscription(input: EpicSetSubscriptionInput!): EpicSetSubscriptionPayload
   epicTreeReorder(input: EpicTreeReorderInput!): EpicTreeReorderPayload
+  issueSetAssignees(input: IssueSetAssigneesInput!): IssueSetAssigneesPayload
   issueSetConfidential(input: IssueSetConfidentialInput!): IssueSetConfidentialPayload
   issueSetDueDate(input: IssueSetDueDateInput!): IssueSetDueDatePayload
   issueSetIteration(input: IssueSetIterationInput!): IssueSetIterationPayload

doc/api/graphql/reference/gitlab_schema.json

@@ -17380,6 +17380,154 @@
           "enumValues": null,
           "possibleTypes": null
         },
+        {
+          "kind": "INPUT_OBJECT",
+          "name": "IssueSetAssigneesInput",
+          "description": "Autogenerated input type of IssueSetAssignees",
+          "fields": null,
+          "inputFields": [
+            {
+              "name": "projectPath",
+              "description": "The project the issue to mutate is in",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "ID",
+                  "ofType": null
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "iid",
+              "description": "The IID of the issue to mutate",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "SCALAR",
+                  "name": "String",
+                  "ofType": null
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "assigneeUsernames",
+              "description": "The usernames to assign to the resource. Replaces existing assignees by default.",
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "LIST",
+                  "name": null,
+                  "ofType": {
+                    "kind": "NON_NULL",
+                    "name": null,
+                    "ofType": {
+                      "kind": "SCALAR",
+                      "name": "String",
+                      "ofType": null
+                    }
+                  }
+                }
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "operationMode",
+              "description": "The operation to perform. Defaults to REPLACE.",
+              "type": {
+                "kind": "ENUM",
+                "name": "MutationOperationMode",
+                "ofType": null
+              },
+              "defaultValue": null
+            },
+            {
+              "name": "clientMutationId",
+              "description": "A unique identifier for the client performing the mutation.",
+              "type": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              },
+              "defaultValue": null
+            }
+          ],
+          "interfaces": null,
+          "enumValues": null,
+          "possibleTypes": null
+        },
+        {
+          "kind": "OBJECT",
+          "name": "IssueSetAssigneesPayload",
+          "description": "Autogenerated return type of IssueSetAssignees",
+          "fields": [
+            {
+              "name": "clientMutationId",
+              "description": "A unique identifier for the client performing the mutation.",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
+            {
+              "name": "errors",
+              "description": "Errors encountered during execution of the mutation.",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "NON_NULL",
+                "name": null,
+                "ofType": {
+                  "kind": "LIST",
+                  "name": null,
+                  "ofType": {
+                    "kind": "NON_NULL",
+                    "name": null,
+                    "ofType": {
+                      "kind": "SCALAR",
+                      "name": "String",
+                      "ofType": null
+                    }
+                  }
+                }
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
+            {
+              "name": "issue",
+              "description": "The issue after mutation",
+              "args": [
+
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "Issue",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            }
+          ],
+          "inputFields": null,
+          "interfaces": [
+
+          ],
+          "enumValues": null,
+          "possibleTypes": null
+        },
         {
           "kind": "INPUT_OBJECT",
           "name": "IssueSetConfidentialInput",
@@ -21772,7 +21920,7 @@
             },
             {
               "name": "assigneeUsernames",
-              "description": "The usernames to assign to the merge request. Replaces existing assignees by default.\n",
+              "description": "The usernames to assign to the resource. Replaces existing assignees by default.",
               "type": {
                 "kind": "NON_NULL",
                 "name": null,
@@ -21794,7 +21942,7 @@
             },
             {
               "name": "operationMode",
-              "description": "The operation to perform. Defaults to REPLACE.\n",
+              "description": "The operation to perform. Defaults to REPLACE.",
               "type": {
                 "kind": "ENUM",
                 "name": "MutationOperationMode",
@@ -24435,6 +24583,33 @@
               "isDeprecated": false,
               "deprecationReason": null
             },
+            {
+              "name": "issueSetAssignees",
+              "description": null,
+              "args": [
+                {
+                  "name": "input",
+                  "description": null,
+                  "type": {
+                    "kind": "NON_NULL",
+                    "name": null,
+                    "ofType": {
+                      "kind": "INPUT_OBJECT",
+                      "name": "IssueSetAssigneesInput",
+                      "ofType": null
+                    }
+                  },
+                  "defaultValue": null
+                }
+              ],
+              "type": {
+                "kind": "OBJECT",
+                "name": "IssueSetAssigneesPayload",
+                "ofType": null
+              },
+              "isDeprecated": false,
+              "deprecationReason": null
+            },
             {
               "name": "issueSetConfidential",
               "description": null,

doc/api/graphql/reference/index.md

@@ -947,6 +947,16 @@ Check permissions for the current user on a issue
 | `reopenIssue` | Boolean! | Indicates the user can perform `reopen_issue` on this resource |
 | `updateIssue` | Boolean! | Indicates the user can perform `update_issue` on this resource |
 
+## IssueSetAssigneesPayload
+
+Autogenerated return type of IssueSetAssignees
+
+| Name  | Type  | Description |
+| ---   |  ---- | ----------  |
+| `clientMutationId` | String | A unique identifier for the client performing the mutation. |
+| `errors` | String! => Array | Errors encountered during execution of the mutation. |
+| `issue` | Issue | The issue after mutation |
+
 ## IssueSetConfidentialPayload
 
 Autogenerated return type of IssueSetConfidential

ee/spec/graphql/mutations/issues/set_assignees_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Mutations::Issues::SetAssignees do
+  it_behaves_like 'a multi-assignable resource' do
+    let_it_be(:resource, reload: true) { create(:issue) }
+  end
+end

ee/spec/graphql/mutations/merge_requests/set_assignees_spec.rb

@@ -3,67 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe Mutations::MergeRequests::SetAssignees do
-  let(:merge_request) { create(:merge_request) }
-  let(:user) { create(:user) }
-
-  subject(:mutation) { described_class.new(object: nil, context: { current_user: user }, field: nil) }
-
-  describe '#resolve' do
-    let(:assignees) { create_list(:user, 3) }
-    let(:assignee_usernames) { assignees.map(&:username) }
-    let(:mutated_merge_request) { subject[:merge_request] }
-
-    subject { mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, assignee_usernames: assignee_usernames) }
-
-    before do
-      assignees.each do |user|
-        merge_request.project.add_developer(user)
-      end
-    end
-
-    context 'when the user can update the merge request' do
-      before do
-        merge_request.project.add_developer(user)
-      end
-
-      it 'sets merge request assignees' do
-        expect(mutated_merge_request).to eq(merge_request)
-        expect(mutated_merge_request.assignees).to match_array(assignees)
-        expect(subject[:errors]).to be_empty
-      end
-
-      it 'removes assignees not in the list' do
-        users = create_list(:user, 2)
-        users.each do |user|
-          merge_request.project.add_developer(user)
-        end
-        merge_request.assignees = users
-        merge_request.save!
-
-        expect(mutated_merge_request).to eq(merge_request)
-        expect(mutated_merge_request.assignees).to match_array(assignees)
-        expect(subject[:errors]).to be_empty
-      end
-
-      context 'when passing "append" as true' do
-        subject { mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, assignee_usernames: assignee_usernames, operation_mode: Types::MutationOperationModeEnum.enum[:append]) }
-
-        let(:existing_assignees) { create_list(:user, 2) }
-
-        before do
-          existing_assignees.each do |user|
-            merge_request.project.add_developer(user)
-          end
-          merge_request.assignees = existing_assignees
-          merge_request.save!
-        end
-
-        it 'does not remove assignees not in the list' do
-          expect(mutated_merge_request).to eq(merge_request)
-          expect(mutated_merge_request.assignees).to match_array(assignees + existing_assignees)
-          expect(subject[:errors]).to be_empty
-        end
-      end
-    end
+  it_behaves_like 'a multi-assignable resource' do
+    let_it_be(:resource, reload: true) { create(:merge_request) }
   end
 end

ee/spec/support/shared_examples/graphql/mutations/set_multiple_assignees_shared_examples.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.shared_examples 'a multi-assignable resource' do
+  let_it_be(:user) { create(:user) }
+
+  subject(:mutation) { described_class.new(object: nil, context: { current_user: user }, field: nil) }
+
+  describe '#resolve' do
+    let_it_be(:assignees) { create_list(:user, 3) }
+    let(:assignee_usernames) { assignees.map(&:username) }
+    let(:mutated_resource) { subject[resource.class.name.underscore.to_sym] }
+
+    subject { mutation.resolve(project_path: resource.project.full_path, iid: resource.iid, assignee_usernames: assignee_usernames) }
+
+    before do
+      assignees.each do |user|
+        resource.project.add_developer(user)
+      end
+    end
+
+    context 'when the user can update the resource' do
+      before do
+        resource.project.add_developer(user)
+      end
+
+      it 'sets the assignees' do
+        expect(mutated_resource).to eq(resource)
+        expect(mutated_resource.assignees).to match_array(assignees)
+        expect(subject[:errors]).to be_empty
+      end
+
+      it 'removes assignees not in the list' do
+        users = create_list(:user, 2)
+        users.each do |user|
+          resource.project.add_developer(user)
+        end
+        resource.assignees = users
+        resource.save!
+
+        expect(mutated_resource).to eq(resource)
+        expect(mutated_resource.assignees).to match_array(assignees)
+        expect(subject[:errors]).to be_empty
+      end
+
+      context 'when passing "append" as true' do
+        subject { mutation.resolve(project_path: resource.project.full_path, iid: resource.iid, assignee_usernames: assignee_usernames, operation_mode: Types::MutationOperationModeEnum.enum[:append]) }
+
+        let(:existing_assignees) { create_list(:user, 2) }
+
+        before do
+          existing_assignees.each do |user|
+            resource.project.add_developer(user)
+          end
+          resource.assignees = existing_assignees
+          resource.save!
+        end
+
+        it 'does not remove assignees not in the list' do
+          expect(mutated_resource).to eq(resource)
+          expect(mutated_resource.assignees).to match_array(assignees + existing_assignees)
+          expect(subject[:errors]).to be_empty
+        end
+      end
+    end
+  end
+end

spec/graphql/mutations/issues/set_assignees_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Mutations::Issues::SetAssignees do
+  it_behaves_like 'an assignable resource' do
+    let_it_be(:resource, reload: true) { create(:issue) }
+  end
+end

spec/graphql/mutations/merge_requests/set_assignees_spec.rb

@@ -3,106 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe Mutations::MergeRequests::SetAssignees do
-  let(:merge_request) { create(:merge_request) }
-  let(:user) { create(:user) }
-
-  subject(:mutation) { described_class.new(object: nil, context: { current_user: user }, field: nil) }
-
-  describe '#resolve' do
-    let(:assignee) { create(:user) }
-    let(:assignee2) { create(:user) }
-    let(:assignee_usernames) { [assignee.username] }
-    let(:mutated_merge_request) { subject[:merge_request] }
-
-    subject { mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, assignee_usernames: assignee_usernames) }
-
-    before do
-      merge_request.project.add_developer(assignee)
-      merge_request.project.add_developer(assignee2)
-    end
-
-    it 'raises an error if the resource is not accessible to the user' do
-      expect { subject }.to raise_error(Gitlab::Graphql::Errors::ResourceNotAvailable)
-    end
-
-    context 'when the user can update the merge request' do
-      before do
-        merge_request.project.add_developer(user)
-      end
-
-      it 'replaces the assignee' do
-        merge_request.assignees = [assignee2]
-        merge_request.save!
-
-        expect(mutated_merge_request).to eq(merge_request)
-        expect(mutated_merge_request.assignees).to contain_exactly(assignee)
-        expect(subject[:errors]).to be_empty
-      end
-
-      it 'returns errors merge request could not be updated' do
-        # Make the merge request invalid
-        merge_request.allow_broken = true
-        merge_request.update!(source_project: nil)
-
-        expect(subject[:errors]).not_to be_empty
-      end
-
-      context 'when passing an empty assignee list' do
-        let(:assignee_usernames) { [] }
-
-        before do
-          merge_request.assignees = [assignee]
-          merge_request.save!
-        end
-
-        it 'removes all assignees' do
-          expect(mutated_merge_request).to eq(merge_request)
-          expect(mutated_merge_request.assignees).to eq([])
-          expect(subject[:errors]).to be_empty
-        end
-      end
-
-      context 'when passing "append" as true' do
-        subject { mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, assignee_usernames: assignee_usernames, operation_mode: Types::MutationOperationModeEnum.enum[:append]) }
-
-        before do
-          merge_request.assignees = [assignee2]
-          merge_request.save!
-
-          # In CE, APPEND is a NOOP as you can't have multiple assignees
-          # We test multiple assignment in EE specs
-          stub_licensed_features(multiple_merge_request_assignees: false)
-        end
-
-        it 'is a NO-OP in FOSS' do
-          expect(mutated_merge_request).to eq(merge_request)
-          expect(mutated_merge_request.assignees).to contain_exactly(assignee2)
-          expect(subject[:errors]).to be_empty
-        end
-      end
-
-      context 'when passing "remove" as true' do
-        before do
-          merge_request.assignees = [assignee]
-          merge_request.save!
-        end
-
-        it 'removes named assignee' do
-          mutated_merge_request = mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, assignee_usernames: assignee_usernames, operation_mode: Types::MutationOperationModeEnum.enum[:remove])[:merge_request]
-
-          expect(mutated_merge_request).to eq(merge_request)
-          expect(mutated_merge_request.assignees).to eq([])
-          expect(subject[:errors]).to be_empty
-        end
-
-        it 'does not remove unnamed assignee' do
-          mutated_merge_request = mutation.resolve(project_path: merge_request.project.full_path, iid: merge_request.iid, assignee_usernames: [assignee2.username], operation_mode: Types::MutationOperationModeEnum.enum[:remove])[:merge_request]
-
-          expect(mutated_merge_request).to eq(merge_request)
-          expect(mutated_merge_request.assignees).to contain_exactly(assignee)
-          expect(subject[:errors]).to be_empty
-        end
-      end
-    end
+  it_behaves_like 'an assignable resource' do
+    let_it_be(:resource, reload: true) { create(:merge_request) }
   end
 end

spec/support/shared_examples/graphql/mutations/set_assignees_shared_examples.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.shared_examples 'an assignable resource' do
+  let_it_be(:user) { create(:user) }
+
+  subject(:mutation) { described_class.new(object: nil, context: { current_user: user }, field: nil) }
+
+  describe '#resolve' do
+    let_it_be(:assignee) { create(:user) }
+    let_it_be(:assignee2) { create(:user) }
+    let(:assignee_usernames) { [assignee.username] }
+    let(:mutated_resource) { subject[resource.class.name.underscore.to_sym] }
+
+    subject { mutation.resolve(project_path: resource.project.full_path, iid: resource.iid, assignee_usernames: assignee_usernames) }
+
+    before do
+      resource.project.add_developer(assignee)
+      resource.project.add_developer(assignee2)
+    end
+
+    it 'raises an error if the resource is not accessible to the user' do
+      expect { subject }.to raise_error(Gitlab::Graphql::Errors::ResourceNotAvailable)
+    end
+
+    context 'when the user can update the resource' do
+      before do
+        resource.project.add_developer(user)
+      end
+
+      it 'replaces the assignee' do
+        resource.assignees = [assignee2]
+        resource.save!
+
+        expect(mutated_resource).to eq(resource)
+        expect(mutated_resource.assignees).to contain_exactly(assignee)
+        expect(subject[:errors]).to be_empty
+      end
+
+      it 'returns errors when resource could not be updated' do
+        allow(resource).to receive(:errors_on_object).and_return(['foo'])
+
+        expect(subject[:errors]).not_to match_array(['foo'])
+      end
+
+      context 'when passing an empty assignee list' do
+        let(:assignee_usernames) { [] }
+
+        before do
+          resource.assignees = [assignee]
+          resource.save!
+        end
+
+        it 'removes all assignees' do
+          expect(mutated_resource).to eq(resource)
+          expect(mutated_resource.assignees).to eq([])
+          expect(subject[:errors]).to be_empty
+        end
+      end
+
+      context 'when passing "append" as true' do
+        subject do
+          mutation.resolve(
+            project_path: resource.project.full_path,
+            iid: resource.iid,
+            assignee_usernames: assignee_usernames,
+            operation_mode: Types::MutationOperationModeEnum.enum[:append]
+          )
+        end
+
+        before do
+          resource.assignees = [assignee2]
+          resource.save!
+
+          # In CE, APPEND is a NOOP as you can't have multiple assignees
+          # We test multiple assignment in EE specs
+          if resource.is_a?(MergeRequest)
+            stub_licensed_features(multiple_merge_request_assignees: false)
+          else
+            stub_licensed_features(multiple_issue_assignees: false)
+          end
+        end
+
+        it 'is a NO-OP in FOSS' do
+          expect(mutated_resource).to eq(resource)
+          expect(mutated_resource.assignees).to contain_exactly(assignee2)
+          expect(subject[:errors]).to be_empty
+        end
+      end
+
+      context 'when passing "remove" as true' do
+        before do
+          resource.assignees = [assignee]
+          resource.save!
+        end
+
+        it 'removes named assignee' do
+          mutated_resource = mutation.resolve(
+            project_path: resource.project.full_path,
+            iid: resource.iid,
+            assignee_usernames: assignee_usernames,
+            operation_mode: Types::MutationOperationModeEnum.enum[:remove]
+          )[resource.class.name.underscore.to_sym]
+
+          expect(mutated_resource).to eq(resource)
+          expect(mutated_resource.assignees).to eq([])
+          expect(subject[:errors]).to be_empty
+        end
+
+        it 'does not remove unnamed assignee' do
+          mutated_resource = mutation.resolve(
+            project_path: resource.project.full_path,
+            iid: resource.iid,
+            assignee_usernames: [assignee2.username],
+            operation_mode: Types::MutationOperationModeEnum.enum[:remove]
+          )[resource.class.name.underscore.to_sym]
+
+          expect(mutated_resource).to eq(resource)
+          expect(mutated_resource.assignees).to contain_exactly(assignee)
+          expect(subject[:errors]).to be_empty
+        end
+      end
+    end
+  end
+end