moving developer-only strings to api/common messages (#10258)

* move translatable string to apiMessages

* use apiMessages instead of res.t for groupIdRequired / keepOrRemove

* move pageMustBeNumber to apiMessages

* change apimessages

* move missingKeyParam to apiMessages

* move more strings to apiMessages

* fix lint

* revert lodash imports to fix tests

* fix webhook test

* fix test

* rollback key change of `keepOrRemove`

* remove unneeded `req.language` param

*  extract more messages from i18n

* add missing `missingTypeParam` message

* Split api- and commonMessages

* fix test

* fix sanity

* merge messages to an object, rename commonMessage to errorMessage

* apiMessages -> apiError, commonMessages -> errorMessage, extract messages to separate objects

* fix test

* module.exports

test/api/v3/unit/libs/apiError.js

@@ -0,0 +1,31 @@
+import apiError from '../../../../../website/server/libs/apiError';
+
+describe('API Messages', () => {
+  const message = 'Only public guilds support pagination.';
+  it('returns an API message', () => {
+    expect(apiError('guildsOnlyPaginate')).to.equal(message);
+  });
+
+  it('throws if the API message does not exist', () => {
+    expect(() => apiError('iDoNotExist')).to.throw;
+  });
+
+  it('clones the passed variables', () => {
+    let vars = {a: 1};
+    sandbox.stub(_, 'clone').returns({});
+    apiError('guildsOnlyPaginate', vars);
+    expect(_.clone).to.have.been.calledOnce;
+    expect(_.clone).to.have.been.calledWith(vars);
+  });
+
+  it('pass the message through _.template', () => {
+    let vars = {a: 1};
+    let stub = sinon.stub().returns('string');
+    sandbox.stub(_, 'template').returns(stub);
+    apiError('guildsOnlyPaginate', vars);
+    expect(_.template).to.have.been.calledOnce;
+    expect(_.template).to.have.been.calledWith(message);
+    expect(stub).to.have.been.calledOnce;
+    expect(stub).to.have.been.calledWith(vars);
+  });
+});