JS code coverage done right. Why?
# installnpm install -g steamshovel# instrumentshovel mySourceDirectory myInstrumentedDirectory# introspectmocha -R steamshovel
For a more detailed guide to the SteamShovel internals, see the API section.
"But I like Blanket/Istanbul/JScover!" I hear you say. "Why should I move?"
That's a great question. It comes down to this:
Your existing instrumentor is lying to you.
That's right. When you run your tests, and the coverage data is collected, the instrumentor only pays attention to whether a code branch was run... or wasn't. Unfortunately this is a gross oversimplification of how code is invoked by a test suite, and it will leave you with a false sense of security.
The hypothesis behind SteamShovel is this:
Your unit tests should run your code directly. Indirect invocation is probably unintentional, and that code shouldn't be considered tested.
In order to support this hypothesis, SteamShovel records the stack depth of the instrumentor at every invocation, and calculates the 'testedness' of a given branch by applying a weighted inverse logarithm to this depth.
This gives you a much more accurate code coverage value. The variance in 'coverage' as defined by SteamShovel and a conventional instrumentor like Istanbul can be as much as 50% — that's how much Istanbul is over-reporting.
SteamShovel can do a whole lot more, too:
csvand you'll get an expression level dump of timing and memory data!
AUTO_INSTRUMENTenvironment variable to
truebefore running the SteamShovel reporter. Remember that this won't instrument code that isn't required, so the manual instrumentor may be more accurate in some cases.
You can override the SteamShovel instrumentor with your own, and record anything you might want to record! The sky is the limit.
Seen here: SteamShovel's recorded memory data from a test run, visualised in, uh... Numbers.app
Because SteamShovel records so much more from your code, it does have a considerable performance impact. However, the accuracy of your test coverage data should be more important than how quickly it runs.
Also, (if you couldn't tell already!) SteamShovel is early in its development. Be careful: there will be an excruciating number of bugs.
I am most of the way through an important refactor which will make steamshovel ready for use by anyone!
You can recursively instrument one or more directories or files by using the SteamShovel instrument processor. This is the same system the CLI tool uses to instrument your code.
var steamshovel = ;steamshovel;
This function takes a string describing an input file or directory, or an array of strings of files/directories. If the first parameter is an array, the second must also be an array, and their lengths must be the same.
The function returns an event emitter, to which it emits the following events:
file) — the processing for one of the directly specified files or directories is complete.
dir) — the processing for a given directory is complete (this is emitted for directories that SteamShovel discovers, too — not just for directly specified trees.)
path/file) — an error was emitted from a filesystem operation.
file) — this file was explicitly ignored (the directive
steamShovel:ignorewas found in the file.)
file) — an error occurred while attempting to instrument a given file (most likely a syntax error.)
path) — emitted when SteamShovel creates a new directory
out) — Emitted when SteamShovel begins processing a new directory
dir) — Emitted after SteamShovel reads the contents of a directory.
file) — Emitted after SteamShovel completes reading a file.
file) — Emitted after SteamShovel completes writing a file.
You can instrument code on a file by file basis by using the
Presently, the code is instrumented by replacing all applicable expressions with
SequenceExpressions (you'll probably know these as lists of expressions
delimited by way of the comma operator.) These make a function call with a
unique ID to the individual expression (incorporating a hash of the filename and
an expression index.)
The filename is required if you want to instrument more than one file. Otherwise you could end up with ID conflicts. (This won't ever be a problem if you let SteamShovel instrument for you.)
The third boolean parameter enables you to turn off the 'map', basically a non-human-readable object definition for the expression instrumentation in the code. It is advisable that you leave this alone, as the code won't run without it, but switching it off can be useful for testing the output of the instrument function.