Improve code quality by increasing code coverage: lib/source-map-from…

…-file.js (bcoe#453)

refactor:  lib/source-map-from-file.js to improve code coverage
refactor: exposed source-map-from-file.js function to write test cases
test: Added two test case cases to cover error handling for improper formatting

lib/report.js

@@ -11,7 +11,7 @@ try {
 const { readdirSync, readFileSync, statSync } = require('fs')
 const { isAbsolute, resolve, extname } = require('path')
 const { pathToFileURL, fileURLToPath } = require('url')
-const getSourceMapFromFile = require('./source-map-from-file')
+const { getSourceMapFromFile } = require('./source-map-from-file')
 // TODO: switch back to @c88/v8-coverage once patch is landed.
 const v8toIstanbul = require('v8-to-istanbul')
 const util = require('util')

lib/source-map-from-file.js

@@ -82,8 +82,13 @@ function sourceMapFromDataUrl (url) {
   const { 0: format, 1: data } = url.split(',')
   const splitFormat = format.split(';')
   const contentType = splitFormat[0]
+  // always evaluates to true for our use cases.  Could possibly be false.
+  // Per https://github.com/bcoe/c8/pull/453#discussion_r1106306167
   const base64 = splitFormat[splitFormat.length - 1] === 'base64'
   if (contentType === 'application/json') {
+    // the data variable is never a json string in the test cases
+    // the upstream branch in node.js still has this logic
+    // https://github.com/nodejs/node/blob/v19.x/lib/internal/source_map/source_map_cache.js#L241
     const decodedData = base64 ? Buffer.from(data, 'base64').toString('utf8') : data
     try {
       return JSON.parse(decodedData)
@@ -97,4 +102,9 @@ function sourceMapFromDataUrl (url) {
   }
 }
 
-module.exports = getSourceMapFromFile
+module.exports = {
+  getSourceMapFromFile,
+  dataFromUrl,
+  sourceMapFromFile,
+  sourceMapFromDataUrl
+}

package.json

@@ -48,6 +48,7 @@
   "devDependencies": {
     "@types/node": "^20.0.0",
     "chai": "^4.3.6",
+    "chai-spies": "^1.0.0",
     "chai-jest-snapshot": "^2.0.0",
     "cross-env": "^7.0.3",
     "mocha": "^9.2.2",

test/integration.js.snap

@@ -156,7 +156,7 @@ hey
 ---------------------------------------|---------|----------|---------|---------|------------------------
 File                                   | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s      
 ---------------------------------------|---------|----------|---------|---------|------------------------
-All files                              |    3.52 |     12.5 |    6.52 |    3.52 |                        
+All files                              |     3.5 |     12.5 |    6.52 |     3.5 |                        
  c8                                    |       0 |        0 |       0 |       0 |                        
   index.js                             |       0 |        0 |       0 |       0 | 1                      
  c8/bin                                |       0 |        0 |       0 |       0 |                        
@@ -168,7 +168,7 @@ All files                              |    3.52 |     12.5 |    6.52 |    3.52
  c8/lib                                |       0 |        0 |       0 |       0 |                        
   parse-args.js                        |       0 |        0 |       0 |       0 | 1-224                  
   report.js                            |       0 |        0 |       0 |       0 | 1-402                  
-  source-map-from-file.js              |       0 |        0 |       0 |       0 | 1-100                  
+  source-map-from-file.js              |       0 |        0 |       0 |       0 | 1-110                  
  c8/lib/commands                       |       0 |        0 |       0 |       0 |                        
   check-coverage.js                    |       0 |        0 |       0 |       0 | 1-70                   
   report.js                            |       0 |        0 |       0 |       0 | 1-43                   
@@ -521,7 +521,7 @@ hey
 ---------------------------------------|---------|----------|---------|---------|------------------------
 File                                   | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s      
 ---------------------------------------|---------|----------|---------|---------|------------------------
-All files                              |    3.52 |     12.5 |    6.52 |    3.52 |                        
+All files                              |     3.5 |     12.5 |    6.52 |     3.5 |                        
  c8                                    |       0 |        0 |       0 |       0 |                        
   index.js                             |       0 |        0 |       0 |       0 | 1                      
  c8/bin                                |       0 |        0 |       0 |       0 |                        
@@ -533,7 +533,7 @@ All files                              |    3.52 |     12.5 |    6.52 |    3.52
  c8/lib                                |       0 |        0 |       0 |       0 |                        
   parse-args.js                        |       0 |        0 |       0 |       0 | 1-224                  
   report.js                            |       0 |        0 |       0 |       0 | 1-402                  
-  source-map-from-file.js              |       0 |        0 |       0 |       0 | 1-100                  
+  source-map-from-file.js              |       0 |        0 |       0 |       0 | 1-110                  
  c8/lib/commands                       |       0 |        0 |       0 |       0 |                        
   check-coverage.js                    |       0 |        0 |       0 |       0 | 1-70                   
   report.js                            |       0 |        0 |       0 |       0 | 1-43                   

test/source-map-from-file.js

@@ -1,7 +1,14 @@
 /* global describe, it */
-const getSourceMapFromFile = require('../lib/source-map-from-file')
+const { getSourceMapFromFile, sourceMapFromDataUrl } = require('../lib/source-map-from-file')
 const assert = require('assert')
 const { readFileSync } = require('fs')
+const chia = require('chai')
+const spies = require('chai-spies')
+
+chia.use(spies)
+
+const { expect } = chia
+
 describe('source-map-from-file', () => {
   it('should parse source maps from compiled targets', () => {
     const sourceMap = getSourceMapFromFile('./test/fixtures/all/ts-compiled/main.js')
@@ -16,4 +23,35 @@ describe('source-map-from-file', () => {
     const sourceMap = getSourceMapFromFile('./test/fixtures/source-maps/inline.js')
     assert.strictEqual(sourceMap.version, 3)
   })
+
+  it('should throw error if source map isn\'t JSON format', () => {
+    const spy = chia.spy
+    spy.on(JSON, 'parse', (content) => {
+      throw new Error('No actual error. Just testing code coverage.  ')
+    })
+    try {
+      getSourceMapFromFile('./test/fixtures/all/ts-compiled/main.js')
+    } finally {
+      expect(JSON.parse).to.have.been.called()
+      spy.restore()
+    }
+
+    spy.on(JSON, 'parse', (content) => {
+      throw new Error('No actual error. Just testing code coverage.  ')
+    })
+    try {
+      const mockUrl = 'application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb...'
+      const sourceMap = sourceMapFromDataUrl(mockUrl)
+      expect(sourceMap).to.equal(null)
+    } finally {
+      expect(JSON.parse).to.have.been.called()
+      spy.restore()
+    }
+  })
+
+  it('should throw error if url doesn\'t have a json content type', () => {
+    const mockUrl = 'application/text;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJzb...'
+    const sourceMap = sourceMapFromDataUrl(mockUrl)
+    expect(sourceMap).to.equal(null)
+  })
 })