Object.prototype manipulations cause weirdness

[isaacs]

Someone send a PR to node-tap that defends against tests that might mutate Object.prototype, essentially replacing some for (var i in obj) loops with Object.keys(obj).forEach(..), or adding a if(obj.hasOwnProperty(i)) guard.

Here's the test:

// test/has-own-property.js
Object.prototype.foo = 'bar'
require('../').pass('modifying Object.prototype did not break things')

Running with coverage does this:

$ nyc node test/has-own-property.js
Transformation error for /Users/isaacs/dev/js/tap/lib/root.js ; return original code
Cannot assign to read only property 'optional' of bar
Transformation error for /Users/isaacs/dev/js/tap/lib/test.js ; return original code
Cannot assign to read only property 'optional' of bar
Transformation error for /Users/isaacs/dev/js/tap/lib/stack.js ; return original code
Cannot assign to read only property 'optional' of bar
Transformation error for /Users/isaacs/dev/js/tap/lib/assert.js ; return original code
Cannot assign to read only property 'optional' of bar
Transformation error for /Users/isaacs/dev/js/tap/lib/synonyms.js ; return original code
Cannot assign to read only property 'optional' of bar
Transformation error for /Users/isaacs/dev/js/tap/lib/mocha.js ; return original code
Cannot assign to read only property 'optional' of bar
TAP version 13
ok 1 - modifying Object.prototype did not break things
1..1
# time=23.336ms
----------|----------|----------|----------|----------|----------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
----------|----------|----------|----------|----------|----------------|
All files |  Unknown |  Unknown |  Unknown |  Unknown |                |
----------|----------|----------|----------|----------|----------------|

I was able to make a simpler example but it has a different error:

// t.js
Object.prototype.foo = 'bar'
require('./x.js')

// x.js
var x = { baz: 1 }

$ nyc node t.js
failed to instrument /Users/isaacs/dev/js/tap/x.js with error: You passed `traverse()` a visitor object with the property "Program" that has the invalid property "foo"
----------|----------|----------|----------|----------|----------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
----------|----------|----------|----------|----------|----------------|
All files |      100 |      100 |      100 |      100 |                |
 t.js     |      100 |      100 |      100 |      100 |                |
----------|----------|----------|----------|----------|----------------|