chore(request_overrider): Update coverage TODOs

I worked on this file quite a bit since this comment was written. At this point the remaining work can be broken out into separate, manageable-seeming todos.

Ref #1404

lib/request_overrider.js

@@ -1,8 +1,5 @@
 'use strict'
 
-// TODO-coverage: This file is puzzling. It would be good to investigate why
-// this works the way it does and add more comments. And coverage too!
-
 const { EventEmitter } = require('events')
 const { IncomingMessage, ClientRequest } = require('http')
 const propagate = require('propagate')
@@ -289,6 +286,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
       timers.setTimeout(emitError, interceptor.getTotalDelay(), error)
       return
     }
+    // TODO-coverage: Either add a test or remove `|| 200` if it's not reachable.
     response.statusCode = Number(interceptor.statusCode) || 200
 
     // Clone headers/rawHeaders to not override them when evaluating later
@@ -329,6 +327,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
         !common.isStream(interceptor.body)
       ) {
         if (interceptor.delayInMs) {
+          // TODO-coverage: Add a test of this error case.
           emitError(
             new Error(
               'Response delay is currently not supported with content-encoded responses.'
@@ -355,6 +354,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
           try {
             responseBody = Buffer.from(responseBody, 'hex')
           } catch (err) {
+            // TODO-coverage: Add a test of this error case.
             debug(
               'exception during Buffer construction from hex data:',
               responseBody,
@@ -378,6 +378,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
     return continueWithResponseBody(null, responseBody)
 
     function continueWithResponseBody(err, responseBody) {
+      // TODO-coverage: Try to find out when this happens and add a test.
       if (continued) {
         return
       }
@@ -397,6 +398,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
         if (Array.isArray(responseBody)) {
           debug('response body is array: %j', responseBody)
 
+          // TODO-coverage: else, throw an error. Add a test.
           if (!isNaN(Number(responseBody[0]))) {
             response.statusCode = Number(responseBody[0])
           }
@@ -437,6 +439,7 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
             response.push(null)
           })
           responseBody.on('error', function(err) {
+            // TODO-coverage: Add a test.
             response.emit('error', err)
           })
         } else if (responseBody && !Buffer.isBuffer(responseBody)) {
@@ -525,11 +528,13 @@ function RequestOverrider(req, options, interceptors, remove, cb) {
           debug('emitting response')
 
           if (typeof cb === 'function') {
+            // TODO-coverage: Find out when this happens and add a test.
             debug('callback with response')
             cb(response)
           }
 
           if (req.aborted) {
+            // TODO-coverage: Add a test of this case.
             emitError(new Error('Request aborted'))
           } else {
             req.emit('response', response)