By default zig build test caches and does not run the tests, unless you set has_side_effects to true.
Example code:
pub fn build(b: *std.Build) void {
const target = b.standardTargetOptions(.{});
const optimize = b.standardOptimizeOption(.{});
const tests = b.addTest(.{
.root_source_file = .{ .path = "src/decimal.zig" },
.target = target,
.optimize = optimize,
.test_runner = "test_runner.zig",
});
const run_tests = b.addRunArtifact(tests);
run_tests.has_side_effects = true;
const test_step = b.step("test", "Run decimal library tests");
test_step.dependOn(&run_tests.step);
}