Add unit tests for trailer

tests/unit/trailer.spec.js

@@ -0,0 +1,48 @@
+const PDFDocument = require('../../');
+
+describe('Document trailer', () => {
+  let document;
+
+  beforeEach(() => {
+    document = new PDFDocument({info: { CreationDate: new Date(Date.UTC(2018,1,1)) } });
+  });
+
+  test('', (done) => {
+    const dataLog = [];
+    const expected = [
+      [
+        '7 0 obj',
+        '<<\n/Producer 8 0 R\n/Creator 9 0 R\n/CreationDate 10 0 R\n>>'
+      ],
+      [
+        '8 0 obj',
+        '(PDFKit)'
+      ],
+      [
+        '9 0 obj',
+        '(PDFKit)'
+      ],
+      [
+        '10 0 obj',
+        '(D:20180201000000Z)'
+      ],
+      [
+        'trailer',
+        `<<\n/Size 11\n/Root 2 0 R\n/Info 7 0 R\n/ID [<8c72cf48ff87daac57e26bf1550e6979> <8c72cf48ff87daac57e26bf1550e6979>]\n>>`
+      ]
+    ];
+    document._write = function(data) {
+      dataLog.push(data)
+    }
+    document.end();
+    setTimeout(() => {
+      for (let i = 0; i < expected.length; ++i) {
+        let idx = dataLog.indexOf(expected[i][0]);
+        for (let j = 1; j < expected[i].length; ++j) {
+          expect(dataLog[idx + j]).toEqual(expected[i][j]);
+        }
+      }
+      done();
+    }, 1);
+  });
+});