Fix Issue #576 collaborator by username

src/main/java/org/kohsuke/github/GHRepository.java

@@ -1022,6 +1022,21 @@ public Set<String> getCollaboratorNames(CollaboratorAffiliation affiliation) thr
         return r;
     }
 
+    /**
+     * Checks if the given user is a collaborator for this repository.
+     *
+     * @param user
+     *            a {@link GHUser}
+     * @return true if the user is a collaborator for this repository
+     * @throws IOException
+     *             the io exception
+     */
+    public boolean isCollaborator(GHUser user) throws IOException {
+        return root().createRequest()
+                .withUrlPath(getApiTailUrl("collaborators/" + user.getLogin()))
+                .fetchHttpStatusCode() == 204;
+    }
+
     /**
      * Obtain permission for a given user in this repository.
      *

src/test/java/org/kohsuke/github/GHRepositoryTest.java

@@ -943,6 +943,13 @@ public void listCollaboratorsFiltered() throws Exception {
         assertThat(filteredCollaborators.size(), lessThan(allCollaborators.size()));
     }
 
+    @Test
+    public void userIsCollaborator() throws Exception {
+        GHRepository repo = getRepository();
+        GHUser collaborator = repo.listCollaborators().toList().get(0);
+        assertThat(repo.isCollaborator(collaborator), is(true));
+    }
+
     @Test
     public void getCheckRuns() throws Exception {
         final int expectedCount = 8;

src/test/resources/org/kohsuke/github/GHRepositoryTest/wiremock/userIsCollaborator/__files/orgs_hub4j-test-org-2.json

@@ -0,0 +1,55 @@
+{
+  "login": "hub4j-test-org",
+  "id": 7544739,
+  "node_id": "MDEyOk9yZ2FuaXphdGlvbjc1NDQ3Mzk=",
+  "url": "https://api.github.com/orgs/hub4j-test-org",
+  "repos_url": "https://api.github.com/orgs/hub4j-test-org/repos",
+  "events_url": "https://api.github.com/orgs/hub4j-test-org/events",
+  "hooks_url": "https://api.github.com/orgs/hub4j-test-org/hooks",
+  "issues_url": "https://api.github.com/orgs/hub4j-test-org/issues",
+  "members_url": "https://api.github.com/orgs/hub4j-test-org/members{/member}",
+  "public_members_url": "https://api.github.com/orgs/hub4j-test-org/public_members{/member}",
+  "avatar_url": "https://avatars.githubusercontent.com/u/7544739?v=4",
+  "description": "Hub4j Test Org Description (this could be null or blank too)",
+  "name": "Hub4j Test Org Name (this could be null or blank too)",
+  "company": null,
+  "blog": "https://hub4j.url.io/could/be/null",
+  "location": "Hub4j Test Org Location (this could be null or blank too)",
+  "email": "hub4jtestorgemail@could.be.null.com",
+  "twitter_username": null,
+  "is_verified": false,
+  "has_organization_projects": true,
+  "has_repository_projects": true,
+  "public_repos": 50,
+  "public_gists": 0,
+  "followers": 0,
+  "following": 0,
+  "html_url": "https://github.com/hub4j-test-org",
+  "created_at": "2014-05-10T19:39:11Z",
+  "updated_at": "2020-06-04T05:56:10Z",
+  "type": "Organization",
+  "total_private_repos": 4,
+  "owned_private_repos": 4,
+  "private_gists": 0,
+  "disk_usage": 11980,
+  "collaborators": 0,
+  "billing_email": "kk@kohsuke.org",
+  "default_repository_permission": "none",
+  "members_can_create_repositories": false,
+  "two_factor_requirement_enabled": false,
+  "members_allowed_repository_creation_type": "none",
+  "members_can_create_public_repositories": false,
+  "members_can_create_private_repositories": false,
+  "members_can_create_internal_repositories": false,
+  "members_can_create_pages": true,
+  "members_can_fork_private_repositories": false,
+  "members_can_create_public_pages": true,
+  "members_can_create_private_pages": true,
+  "plan": {
+    "name": "free",
+    "space": 976562499,
+    "private_repos": 10000,
+    "filled_seats": 38,
+    "seats": 3
+  }
+}