feat(plugins): run verifications in series

With this new feature you can pass an array of plugin locations/names to
both "verifyConditions" and "verifyRelease" in your `package.json`'s "release"
field. This will run multiple verification plugins in series.

test/mocks/plugin-error-a.js

@@ -0,0 +1,3 @@
+module.exports = function (config, options, cb) {
+  cb(new Error('a'))
+}

test/mocks/plugin-error-b.js

@@ -0,0 +1,3 @@
+module.exports = function (config, options, cb) {
+  cb(new Error('b'))
+}

test/mocks/plugin-result-a.js

@@ -0,0 +1,3 @@
+module.exports = function (config, options, cb) {
+  cb(null, 'a')
+}

test/mocks/plugin-result-b.js

@@ -0,0 +1,3 @@
+module.exports = function (config, options, cb) {
+  cb(null, 'b')
+}

test/specs/plugins.js

@@ -3,7 +3,7 @@ const test = require('tap').test
 const plugins = require('../../dist/lib/plugins')
 
 test('export plugins', (t) => {
-  t.plan(4)
+  t.plan(5)
 
   const defaultPlugins = plugins({})
 
@@ -11,6 +11,59 @@ test('export plugins', (t) => {
   t.is(typeof defaultPlugins.generateNotes, 'function')
   t.is(typeof defaultPlugins.verifyConditions, 'function')
   t.is(typeof defaultPlugins.verifyRelease, 'function')
+  t.is(typeof defaultPlugins.getLastRelease, 'function')
+})
+
+test('plugin pipelines', (t) => {
+  t.plan(3)
+
+  t.test('get all results', (tt) => {
+    const pipelinePlugins = plugins({
+      verifyRelease: [
+        './dist/lib/plugin-noop',
+        './.test/mocks/plugin-result-a',
+        './.test/mocks/plugin-result-b'
+      ]
+    })
+
+    pipelinePlugins.verifyRelease({}, (err, results) => {
+      tt.error(err)
+      tt.same(results, [undefined, 'a', 'b'])
+      tt.end()
+    })
+  })
+
+  t.test('get first error', (tt) => {
+    const pipelinePlugins = plugins({
+      verifyConditions: [
+        './dist/lib/plugin-noop',
+        './.test/mocks/plugin-error-a',
+        './.test/mocks/plugin-error-b'
+      ]
+    })
+
+    pipelinePlugins.verifyConditions({}, (err) => {
+      tt.is(err.message, 'a')
+      tt.end()
+    })
+  })
+
+  t.test('get error and only results before', (tt) => {
+    const pipelinePlugins = plugins({
+      verifyRelease: [
+        './dist/lib/plugin-noop',
+        './.test/mocks/plugin-result-a',
+        './.test/mocks/plugin-error-b',
+        './.test/mocks/plugin-result-b'
+      ]
+    })
+
+    pipelinePlugins.verifyRelease({}, (err, results) => {
+      tt.is(err.message, 'b')
+      tt.same(results, [undefined, 'a', undefined])
+      tt.end()
+    })
+  })
 })
 
 test('normalize and load plugin', (t) => {