generate coverage fixture without source maps

It can't be used to test source map support if the source maps are already
applied to the coverage report.

With this change no reports are written to disk. Therefore the temp directory
doesn't have to be cleaned.

test/fixtures/_generateCoverage.js

@@ -14,14 +14,9 @@ var NYC = require('../../')
 // Load the 'branching' source map fixture.
 var fixture = require('source-map-fixtures').inline('branching')
 
-// Prevent pollution from earlier nyc runs.
-var tempDirectory = path.join(__dirname, '.nyc_output')
-rimraf.sync(tempDirectory)
-
 // Inject nyc into this process.
 var nyc = (new NYC({
-  cwd: path.join(__dirname, '..', '..'),
-  tempDirectory: tempDirectory
+  cwd: path.join(__dirname, '..', '..')
 })).wrap()
 // Override the exclude option, source-map-fixtures is inside node_modules but
 // should not be excluded when generating the coverage report.
@@ -31,18 +26,23 @@ nyc.exclude = []
 // coverage.
 fixture.require().run()
 
-// Write the coverage file so reports can be loaded.
-nyc.writeCoverageFile()
+// Copy NYC#writeCoverageFile() behavior to get the coverage object, before
+// source maps have been applied.
+var coverage = global.__coverage__
+if (typeof __coverage__ === 'object') coverage = __coverage__
+if (!coverage) {
+  console.error('No coverage.')
+  process.exit(1)
+}
 
-var reports = _.values(nyc._loadReports()[0])
+var reports = _.values(coverage)
 if (reports.length !== 1) {
   console.error('Expected 1 report to be generated, got ' + reports.length)
   process.exit(1)
 }
 
-var coverage = reports[0]
 fs.writeFileSync(
   path.join(__dirname, 'coverage.js'),
   '// Generated using node test/fixtures/_generateCoverage.js\n' +
-  'exports[' + JSON.stringify(coverage.path) + '] = ' + JSON.stringify(coverage, null, 2) + '\n')
-console.log('Written coverage report.')
+  'exports[' + JSON.stringify(reports[0].path) + '] = ' + JSON.stringify(reports[0], null, 2) + '\n')
+  console.log('Written coverage report.')