fix: tests

- Fixes the `important` prop of DeclarationProps, which should be optional.
- Adds a test for the `assign` method.

lib/declaration.d.ts

@@ -32,7 +32,7 @@ export interface DeclarationProps {
   /** Value of the declaration. */
   value: string
   /** Whether the declaration has an `!important` annotation. */
-  important: boolean
+  important?: boolean
   /** Information used to generate byte-to-byte equal node string as it was in the origin input. */
   raws?: DeclarationRaws
 }

test/node.test.ts

@@ -162,6 +162,18 @@ it('toString() accepts custom syntax', () => {
   expect(new Rule({ selector: 'a' }).toString({ stringify })).toEqual('a')
 })
 
+it('assign() assigns to node', () => {
+  let decl = new Declaration({ prop: 'white-space', value: 'overflow-wrap' })
+
+  expect(decl.prop).toBe('white-space')
+  expect(decl.value).toBe('overflow-wrap')
+
+  decl.assign({ prop: 'word-wrap', value: 'break-word' })
+
+  expect(decl.prop).toBe('word-wrap')
+  expect(decl.value).toBe('break-word')
+})
+
 it('clone() clones nodes', () => {
   let rule = new Rule({ selector: 'a' })
   rule.append({ prop: 'color', value: '/**/black' })