go-mockery: add package test

Add a very basic package test for go-mockery that asserts:
* version matches what is expected
* running the program generates a *.go file

Co-authored-by: Sandro <sandro.jaeckel@gmail.com>

pkgs/development/tools/go-mockery/default.nix

@@ -1,4 +1,4 @@
-{ lib, buildGoModule, fetchFromGitHub }:
+{ lib, buildGoModule, fetchFromGitHub, go-mockery, runCommand, go }:
 
 buildGoModule rec {
   pname = "go-mockery";
@@ -24,6 +24,37 @@ buildGoModule rec {
 
   vendorHash = "sha256-Dl8Q6fQa7BKp06a4OT82+wHYQRN1aWZ2qK25GzhOw8A=";
 
+  passthru.tests = {
+    generateMock = runCommand "${pname}-test" {
+      nativeBuildInputs = [ go-mockery ];
+      buildInputs = [ go ];
+    } ''
+      if [[ $(mockery --version) != *"${version}"* ]]; then
+        echo "Error: program version does not match package version"
+        exit 1
+      fi
+
+      export HOME=$TMPDIR
+
+      cat <<EOF > foo.go
+      package main
+
+      type Foo interface {
+        Bark() string
+      }
+      EOF
+
+      mockery --name Foo --dir .
+
+      if [[ ! -f "mocks/Foo.go" ]]; then
+        echo "Error: mocks/Foo.go was not generated by ${pname}"
+        exit 1
+      fi
+
+      touch $out
+    '';
+  };
+
   meta = with lib; {
     homepage = "https://github.com/vektra/mockery";
     description = "A mock code autogenerator for Golang";