diff --git a/validators/__tests__/headerFields.spec.js b/validators/__tests__/headerFields.spec.js
new file mode 100644
index 000000000..23a18b686
--- /dev/null
+++ b/validators/__tests__/headerFields.spec.js
@@ -0,0 +1,65 @@
+const assert = require('chai').assert
+const { collect39Issues } = require('../headerFields')
+
+describe('headerFields', () => {
+  describe('collect39Issues()', () => {
+    it('should return an empty array if there are no files in allIssues39Dict', () => {
+      const allIssues39Dict = {}
+      const issues = collect39Issues(allIssues39Dict)
+      assert.isArray(issues)
+      assert.lengthOf(issues, 0)
+    })
+    it('should return one issue per file in the allIssues39Dict', () => {
+      const allIssues39Dict = {
+        file_1: [
+          {
+            code: 39,
+            reason: 'for some reason',
+          },
+          {
+            code: 39,
+            reason: 'for some other reason',
+          },
+        ],
+      }
+      const issues = collect39Issues(allIssues39Dict)
+      assert.isArray(issues)
+      assert.lengthOf(issues, 1)
+    })
+    it('should return one issue for each file with code 39 issues', () => {
+      const allIssues39Dict = {
+        file_1: [
+          {
+            code: 39,
+            reason: 'reason1',
+          },
+        ],
+        file_2: [
+          {
+            code: 39,
+            reason: 'reason2',
+          },
+        ],
+      }
+      const issues = collect39Issues(allIssues39Dict)
+      assert.lengthOf(issues, 2)
+    })
+    it('constructs a combined reason string from each issue.reason of a file', () => {
+      const allIssues39Dict = {
+        file_1: [
+          {
+            code: 39,
+            reason: 'reason1',
+          },
+          {
+            code: 39,
+            reason: 'reason2',
+          },
+        ],
+      }
+      const issues = collect39Issues(allIssues39Dict)
+      assert.lengthOf(issues, 1)
+      assert(issues[0].reason == ' reason1 reason2')
+    })
+  })
+})
diff --git a/validators/headerFields.js b/validators/headerFields.js
index e1a344dd0..9dd532996 100644
--- a/validators/headerFields.js
+++ b/validators/headerFields.js
@@ -12,7 +12,7 @@ var Issue = utils.issues.Issue
  * arrays more arguments will need to be added to headerField.
  */
 
-var headerFields = function headerFields(headers) {
+const headerFields = headers => {
   var finalIssues = []
   var allIssues39Dict = {}
   var fields = ['dim', 'pixdim']
@@ -34,18 +34,22 @@ var headerFields = function headerFields(headers) {
     }
   }
 
-  for (let file in allIssues39Dict) {
-    if (allIssues39Dict.hasOwnProperty(file)) {
-      const firstIssue = allIssues39Dict[file][0]
-      let evidence = ''
-      for (var issue of allIssues39Dict[file]) {
-        evidence = evidence + ' ' + allIssues39Dict[file][issue].reason
-      }
-      firstIssue.reason = evidence
-      finalIssues.push(firstIssue)
+  finalIssues = finalIssues.concat(collect39Issues(allIssues39Dict))
+
+  return finalIssues
+}
+
+const collect39Issues = allIssues39Dict => {
+  const finalIssues = []
+  for (let file of Object.keys(allIssues39Dict)) {
+    const firstIssue = allIssues39Dict[file][0]
+    let evidence = ''
+    for (var issue of allIssues39Dict[file]) {
+      evidence = evidence + ' ' + issue.reason
     }
+    firstIssue.reason = evidence
+    finalIssues.push(firstIssue)
   }
-
   return finalIssues
 }
 
@@ -58,7 +62,7 @@ var headerFields = function headerFields(headers) {
  * dimensionality of similar anatomy/functional/dwi headers are being compared.
  */
 
-var headerField = function headerField(headers, field) {
+const headerField = (headers, field) => {
   var nifti_types = {}
   var issues = {}
   for (var header_index = 0; header_index < headers.length; header_index++) {
@@ -249,7 +253,7 @@ var headerField = function headerField(headers, field) {
  * errors that cause resolutions to be slightly different. Returns true if
  * the two headers are signifigantly different
  */
-function headerFieldCompare(header1, header2) {
+const headerFieldCompare = (header1, header2) => {
   var hdr1 = header1.split(',')
   var hdr2 = header2.split(',')
   if (hdr1.length !== hdr2.length) {
@@ -272,3 +276,4 @@ function headerFieldCompare(header1, header2) {
 }
 
 module.exports = headerFields
+module.exports.collect39Issues = collect39Issues