chore(tests): add test for renderer

tests/unit/core/renderer_spec.lua

@@ -0,0 +1,47 @@
+local spy = require('luassert.spy')
+local renderer = require('vgit.core.renderer')
+
+describe('renderer', function()
+  local buffer = { bufnr = 1, on_render = function() end }
+
+  before_each(function()
+    renderer.buffers = {}
+    renderer.registered = false
+  end)
+
+  describe('register_module', function()
+    it('should register the module if not already registered', function()
+      local spy_vim_set_decoration_provider = spy.on(vim.api, 'nvim_set_decoration_provider')
+
+      renderer.register_module()
+
+      assert.is_true(renderer.registered)
+      assert.spy(spy_vim_set_decoration_provider).was.called()
+    end)
+
+    it('should not register the module if already registered', function()
+      local spy_vim_set_decoration_provider = spy.on(vim.api, 'nvim_set_decoration_provider')
+
+      renderer.registered = true
+      renderer.register_module()
+
+      assert.is_true(renderer.registered)
+      assert.spy(spy_vim_set_decoration_provider).was_not.called()
+    end)
+  end)
+
+  describe('attach', function()
+    it('should attach a buffer', function()
+      renderer.attach(buffer)
+      assert.is_not_nil(renderer.buffers[buffer.bufnr])
+    end)
+  end)
+
+  describe('detach', function()
+    it('should detach a buffer', function()
+      renderer.attach(buffer)
+      renderer.detach(buffer)
+      assert.is_nil(renderer.buffers[buffer.bufnr])
+    end)
+  end)
+end)