Refactor model tests to use rspec's be_valid/be_invalid

spec/models/board_spec.rb

@@ -5,23 +5,27 @@ RSpec.describe Board, type: :model do
   let(:board) { FactoryBot.create(:board) }
   let(:noname_board) { FactoryBot.build(:noname_board) }
 
+  it 'should be valid' do
+    expect(board).to be_valid
+  end
+
   it 'has a non-nil name' do
-    expect(noname_board.valid?).to be_falsy
+    expect(noname_board).to be_invalid
   end
 
   it 'has an unique name' do
     board
     board2 = Board.new(name: board.name, description: "This board has the same name as board!")
 
-    expect(board2.valid?).to be_falsy
+    expect(board2).to be_invalid
   end
 
   it 'has a description that can be nil or empty' do
     nildescription_board = Board.new(name: "nil board", description: nil)
     emptydescription_board = Board.new(name: "empty board", description: "")
 
-    expect(nildescription_board.valid?).to be_truthy
-    expect(emptydescription_board.valid?).to be_truthy
+    expect(nildescription_board).to be_valid
+    expect(emptydescription_board).to be_valid
   end
 
 end