Display more useful errors

#11

__tests__/validate-title.js

@@ -8,7 +8,7 @@
 
 const t = require('assert');
 
-const isValidTitle = require('../validate-title.js');
+const validateTitle = require('../validate-title.js');
 
 test('valid commits pass', () => {
   const valid = [
@@ -42,7 +42,7 @@ test('valid commits pass', () => {
   ];
 
   valid.forEach(msg => {
-    t.equal(isValidTitle(msg), true, `"${msg}", was expected to be valid`);
+    t.equal(validateTitle(msg).length, 0, `"${msg}", was expected to be valid`);
   });
 });
 
@@ -65,6 +65,6 @@ test('invalid commits fail', () => {
   ];
 
   invalid.forEach(msg => {
-    t.equal(isValidTitle(msg), false);
+    t.notEqual(validateTitle(msg).length, 0);
   });
 });

index.js

@@ -4,7 +4,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-const isValidTitle = require('./validate-title.js');
+const validateTitle = require('./validate-title.js');
 
 module.exports = robot => {
   robot.on('pull_request.opened', check);
@@ -13,23 +13,24 @@ module.exports = robot => {
 
   async function check(context) {
     const pr = context.payload.pull_request;
-    const passed = isValidTitle(pr.title);
-    setStatus(context, passed);
+    const errors = validateTitle(pr.title);
+    setStatus(context, errors);
   }
 };
 
-function setStatus(context, passing) {
+function setStatus(context, errors) {
   const {github} = context;
 
-  const status = passing
-    ? {
-        state: 'success',
-        description: 'PR title is valid',
-      }
-    : {
-        state: 'failure',
-        description: 'PR title is invalid',
-      };
+  const status =
+    errors.length === 0
+      ? {
+          state: 'success',
+          description: 'PR title is valid',
+        }
+      : {
+          state: 'failure',
+          description: 'PR title is invalid:\n' + errors.join('\n'),
+        };
 
   github.repos.createStatus(
     context.repo({

validate-title.js

@@ -6,27 +6,28 @@
 
 const nlp = require('compromise');
 
-module.exports = function isValidTitle(text) {
+module.exports = function validateTitle(text) {
   const parsed = nlp(text);
-  return isValidSentence(parsed) && firstTermIsValidVerb(parsed);
+  return [...validateSentence(parsed), ...validateFirstTerm(parsed)];
 };
 
 // Validate text is a single sentence with no end punctuation
-function isValidSentence(parsed) {
+function validateSentence(parsed) {
   const sentences = parsed.sentences();
-  // must be one and only one sentence
-  if (sentences.length !== 1) {
-    return false;
-  }
-  // must be at least two words long
-  if (parsed.terms().length < 2) {
-    return false;
-  }
-  // must not have any end punctuation
-  if (sentences.list[0].endPunctuation() !== null) {
-    return false;
-  }
-  return true;
+  return [
+    !isSingleSentence(sentences) ? 'Must be one and only one sentence.' : null,
+    !isNotTooShort(parsed) ? 'Must be at least two words long.' : null,
+    !isNotPunctuated(sentences) ? 'Must not have any end punctuation.' : null,
+  ].filter(Boolean);
+}
+
+// Validate first word is a capitalized imperative mood verb
+function validateFirstTerm(parsed) {
+  const term = parsed.terms().data()[0];
+  return [
+    !isValidVerb(term) ? 'First word must be imperative verb.' : null,
+    !isCapitalized(term) ? 'First word must be capitalized.' : null,
+  ].filter(Boolean);
 }
 
 // The following verbs starting with `re` are categorized as singular nouns
@@ -47,10 +48,16 @@ const nounWhitelist = new Set([
   'upgrade',
 ]);
 
-// Validate first word is a capitalized imperative mood verb
-function firstTermIsValidVerb(parsed) {
-  const term = parsed.terms().data()[0];
-  return isValidVerb(term) && isCapitalized(term);
+function isSingleSentence(sentences) {
+  return sentences.length === 1;
+}
+
+function isNotTooShort(parsed) {
+  return parsed.terms().length >= 2;
+}
+
+function isNotPunctuated(sentences) {
+  return sentences.list[0].endPunctuation() === null;
 }
 
 function isValidVerb(term) {