# git-check-assertions

🚧 Merely a proof-of-concept right now.

I recently wrote two blogs posts arguing that there might be some value in writing verifiable claims, i.e. assertions, inside of our commit messages:

* [Should we start writing verifiable claims in commit message?](https://sven.memcmp.org/2026-02-19-should-we-start-writing-verifiable-claims-in-commit-messages/)
* [Writing the steps to validate a test in the commit message](https://sven.memcmp.org/2026-02-20-writing-the-steps-to-validate-a-test-in-the-commit-message/)

This is a simple verifier for such assertions.

You include a small bash script inside your commit messages, and `git-check-assertions` will then check out every commit (from the point that your branch diverged from `main`), and verify that the script in the commit message runs successfully.

⚠️ Only run this on repositories and branches that you trust, since the `bash` scripts in the commit messages can do whatever they want.

## Installation

On most systems, clone this repository and add the `bin` directory to your `PATH`.

If you use Nix with flakes, you can simply add it to your program's devshell instead:

```diff
@@ -2,12 +2,18 @@
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
     flake-utils.url = "github:numtide/flake-utils";
+    git-check-assertions = {
+      url = "git+https://codeberg.org/svenvanheugten/git-check-assertions.git?ref=main";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.flake-utils.follows = "flake-utils";
+    };
   };
   outputs =
     {
       self,
       nixpkgs,
       flake-utils,
+      git-check-assertions,
     }:
     flake-utils.lib.eachDefaultSystem (
       system:
@@ -17,7 +23,7 @@
       {
         packages.default = pkgs.callPackage ./default.nix { };
         devShells.default = pkgs.mkShell {
-          packages = [ ];
+          packages = [ git-check-assertions.packages.${system}.default ];
         };
       }
     )
```

## Examples of commit messages

Assert that a commit builds:

~~~
```git-check-assertions
dotnet build
```
~~~

Assert that a commit builds and that the tests succeed:

~~~
```git-check-assertions
dotnet build
dotnet test --no-build
```
~~~

Assert that a commit builds, but that the tests do not succeed:

~~~
```git-check-assertions
dotnet build
run dotnet test --no-build
assert_failure
```
~~~

Assert that a commit builds, and that the tests fail with exactly the error that you expect:

~~~
```git-check-assertions
dotnet build
run dotnet test --no-build
assert_failure
assert_output --partial "Invalid URL"
```
~~~

Assert that a commit builds, and that a specific change breaks the tests (as discussed [here](https://sven.memcmp.org/2026-02-20-writing-the-steps-to-validate-a-test-in-the-commit-message/)):

~~~
```git-check-assertions
dotnet test
sed -i '/crucial code/d' Main.fs
dotnet build
run dotnet test --no-build
assert_failure
```
~~~