Proof for VS Code
See which of your passing tests actually prove anything, inline as you
code.
Coverage tells you a line executed. It doesn't tell you that anything
checked what that line did. This extension runs proof-java
against your workspace and shows its verdict directly in the editor: which
lines are covered, which of the tests covering them have no real assertion,
and, when you ask for it, which mutations nothing catches.
Works in VS Code, Cursor, and Windsurf.
Why
A green test suite and a high coverage percentage both quietly assume the
same thing: that the code checking your program actually works. It's
common for that assumption to be wrong: a test with no assertion, a test
that compares a constant to itself, a test whose only checks sit inside a
try block that swallows the exception. All three run green. All three
raise your coverage number. None of them would catch a real bug.
Proof reads the evidence your build already produces (a JaCoCo report, your
git diff, and optionally a PIT mutation run) and turns it into specific
findings, shown where you're already looking: the editor gutter, a hover,
the Problems panel.
Features
- Coverage gutter: inline, colored by line. Covered, partially
covered, uncovered, excluded, or oracleless (covered, but by tests with
no real assertion), each with its own distinct color, because "covered"
and "meaningfully tested" are not the same claim.
- Explorer badges: coverage percentage on every file and folder in
the file tree, rolled up from the same data as the gutter.
- Line → Tests: for the file you have open, which tests cover a given
line, and whether each one has a real oracle. In a test file, the same
view runs in reverse, showing which production lines this test
actually exercises.
- Test Quality view: every finding (no assertion, tautological
assertion, swallowed exception, null-check-only, and more), filterable
and groupable by rule or by file, with a plain-language explanation for
each.
- Mutation testing: run PIT against a single class (usually a few
seconds) or a whole module (minutes, behind a confirmation, since it can
run long). Results: class → method → mutant → the tests that failed to
kill it, with live progress.
- Problems panel integration: every finding also shows up as a
standard VS Code diagnostic, so it participates in the usual
navigation/quick-fix flow.
- HTML export: a single, offline HTML report of the current results,
for sharing outside the editor.
- Every number comes from the CLI's own JSON. The extension never parses
coverage XML, runs git, or computes a percentage itself.
Screenshots
Line → Tests: which tests cover this line, and whether each one has a
real oracle (a test file open shows the reverse: which lines this test
actually exercises).
Test Quality: every finding, filterable and groupable by rule or file.
Mutation: class → method → mutant → the tests that failed to kill it,
with live progress on a run.
Requirements
- A Maven or Gradle project with a JaCoCo report. Quick Scan finds either
target/site/jacoco/jacoco.xml (Maven) or
build/reports/jacoco/test/jacocoTestReport.xml (Gradle) automatically.
Run Tests, Deep Scan, and Mutation Testing all work for a plain-Java
Gradle project too, provided it has a committed Gradle Wrapper
(gradlew/gradlew.bat) - this extension only ever runs a project's
own pinned wrapper, never a bare gradle on PATH. See
proof-java's own README for
the full build-tool support matrix (including Android/Kotlin gaps).
proof-java.jar: the CLI this extension runs. See
proof-java for what it does
and how it works. The extension can fetch the jar for you (see Usage
below); you never need to clone or build that repository yourself just
to use this extension.
Installation
Search for Proof in the VS Code Extensions view, or install it from
the Marketplace listing.
To build it from source instead, see CONTRIBUTING.md.
Usage
- Open your project in VS Code and open the Proof icon in the
Activity Bar. If
proof-java.jar isn't already on your machine, run
Proof: Download proof-java.jar (Command Palette or the Run panel).
It fetches the latest release from
proof-java, verifies it
against the published checksum, and installs it somewhere the
extension already knows to look (no setting to configure). Already
have a jar elsewhere? Point proof.jarPath at it instead.
- Run Quick Scan for coverage and oracle findings, Deep Scan to
also collect per-test line evidence, or right-click a file and choose
Mutation Test This Class for mutation results on just that class.
- Click through the Coverage / Test Quality / Line → Tests / Mutation
views, or just read the gutter and hover over a line.
Configuration
The most commonly changed settings (search proof. in Settings for the
full list):
| Setting |
Default |
Purpose |
proof.jarPath |
(auto-detected) |
Path to proof-java.jar, if it isn't in one of the default locations |
proof.diffMode |
uncommitted |
What counts as "changed": no-vcs, uncommitted, or base |
proof.baseRef |
(none) |
The ref to diff against when diffMode is base |
proof.badgeMetric |
sonar-compatible |
Which of the three coverage modes drives the gutter/badges |
proof.show.oraclelessLines |
true |
Highlight covered-but-unasserted lines separately |
proof.mutationTimeout |
300 |
Per-module time budget (seconds) for mutation testing |
Documentation
CONTRIBUTING.md: building, running, and testing
the extension itself.- proof-java: the CLI this extension runs, and
what each finding actually means.
skills/proof-java:
if you use an AI coding agent to write or repair tests, this is a skill
for it. It runs proof-java, reads the verdict JSON, and acts on the
findings in a loop instead of guessing whether a test is good.
License
Apache-2.0, the same license as
proof-java.
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