diff --git a/src/lib/unit/caller.js b/src/lib/unit/caller.js
new file mode 100644
index 0000000..a11d8cc
--- /dev/null
+++ b/src/lib/unit/caller.js
@@ -0,0 +1,28 @@
+const { isPromise } = require('../../util');
+
+const caller = (test, state) => {
+
+	let value, error;
+	try {
+		value = test(state);
+	} catch (e) {
+		error = e;
+	}
+
+	const promise = isPromise(value);
+
+	if (promise) {
+		return value
+		.then(res => ({ resolve: res, promise: true }))
+		.catch(rej => ({ rejection: rej, promise: true }));
+	} else {
+		return Promise.resolve({
+			...(!error && {value}),
+			...(error && {error}),
+			promise: false,
+		});
+	}
+
+};
+
+module.exports = caller;