Added test coverage for 'subscribed' transform

refs https://github.com/TryGhost/Toolbox/issues/430

- Not having any extra logic in the mapper will allow to have a generalized "mapping" concept for CSV input serialization
- This is groundwork for stricter header value filtering on the parsing stage

ghost/members-csv/lib/parse.js

@@ -4,18 +4,20 @@ const papaparse = require('papaparse');
 const fs = require('fs-extra');
 
 module.exports = (path, mapping, defaultLabels = []) => {
+    const inputMapping = Object.assign({}, mapping, {
+        subscribed_to_emails: 'subscribed'
+    });
+
     return new Promise(function (resolve, reject) {
         const csvFileStream = fs.createReadStream(path);
         const csvParserStream = papaparse.parse(papaparse.NODE_STREAM_INPUT, {
             header: true,
             transformHeader(_header) {
                 let header = _header;
-                if (mapping && Reflect.has(mapping, _header)) {
-                    header = mapping[_header];
-                }
-                if (header === 'subscribed_to_emails') {
-                    return 'subscribed';
+                if (inputMapping && Reflect.has(inputMapping, _header)) {
+                    header = inputMapping[_header];
                 }
+
                 return header;
             },
             transform(value, header) {

ghost/members-csv/test/fixtures/subscribed-to-emails-header.csv

@@ -0,0 +1,3 @@
+email,subscribed_to_emails
+jbloggs@example.com,true
+test@example.com,false

ghost/members-csv/test/parse.test.js

@@ -1,5 +1,6 @@
 const should = require('should');
 const path = require('path');
+const assert = require('assert');
 const {parse} = require('../index');
 const csvPath = path.join(__dirname, '/fixtures/');
 
@@ -122,4 +123,18 @@ describe('parse', function () {
         result[1].email.should.eql('test@example.com');
         should.equal(result[1].name, null);
     });
+
+    it('read csv: transforms "subscribed_to_emails" column to "subscribed" property', async function () {
+        const result = await readCSV({
+            filePath: csvPath + 'subscribed-to-emails-header.csv'
+        });
+
+        assert.ok(result);
+        assert.equal(result.length, 2);
+        assert.equal(result[0].email, 'jbloggs@example.com');
+        assert.ok(result[0].subscribed);
+
+        assert.equal(result[1].email, 'test@example.com');
+        assert.equal(result[1].subscribed, false);
+    });
 });