diff --git a/dune-workspace b/dune-workspace
new file mode 100644
index 0000000..a017b55
--- /dev/null
+++ b/dune-workspace
@@ -0,0 +1,2 @@
+(lang dune 3.12)
+(instrument_with bisect_ppx)
\ No newline at end of file
diff --git a/flake.nix b/flake.nix
index 99af3a7..46b9ebb 100644
--- a/flake.nix
+++ b/flake.nix
@@ -30,6 +30,8 @@
             inputsFrom = [ self'.packages.default ];
             packages = [
               pkgs.just
+              pkgs.ocamlPackages.alcotest
+              pkgs.ocamlPackages.bisect_ppx
               pkgs.ocamlPackages.dune_3
               pkgs.ocamlPackages.findlib
               pkgs.ocamlPackages.ocaml
diff --git a/lib/dune b/lib/dune
index 6e33744..e268194 100644
--- a/lib/dune
+++ b/lib/dune
@@ -1,5 +1,13 @@
 (library
   (name lib)
   (public_name flake_env.lib)
-  (libraries core core_unix core_unix.filename_unix core_unix.sys_unix ppx_yojson_conv re sha)
-  (preprocess (pps ppx_yojson_conv ppx_jane ppx_inline_test)))
\ No newline at end of file
+  (libraries
+    core
+    core_unix
+    core_unix.filename_unix
+    core_unix.sys_unix
+    ppx_yojson_conv
+    re
+    sha)
+  (instrumentation (backend bisect_ppx))
+  (preprocess (pps ppx_yojson_conv ppx_jane )))
\ No newline at end of file
diff --git a/tests/dune b/tests/dune
new file mode 100644
index 0000000..9440d3f
--- /dev/null
+++ b/tests/dune
@@ -0,0 +1,13 @@
+(tests
+  (names
+    flake_env_test_versions
+    flake_env_test_watches
+    flake_env_test_util)
+  (deps spit_version.sh)
+  (libraries
+    lib
+    alcotest
+    core
+    core_unix
+    core_unix.sys_unix
+    core_unix.filename_unix))
\ No newline at end of file
diff --git a/tests/flake_env_test_util.re b/tests/flake_env_test_util.re
new file mode 100644
index 0000000..6f8e11f
--- /dev/null
+++ b/tests/flake_env_test_util.re
@@ -0,0 +1,159 @@
+open Core;
+module Unix = Core_unix;
+
+open Lib.Util;
+
+let _pp_exit_or_signal = (pp_fmt, e) =>
+  Fmt.pf(pp_fmt, "%s", Unix.Exit_or_signal.to_string_hum(e));
+let _exit_or_signal_eq = (a, b) => Unix.Exit_or_signal.compare(a, b) == 0;
+let testable_exit_or_signal =
+  Alcotest.testable(_pp_exit_or_signal, _exit_or_signal_eq);
+
+let _syst_to_bool =
+  fun
+  | `Yes => true
+  | _ => false;
+
+let check_exit_or_signal =
+  Alcotest.(check(Alcotest.pair(testable_exit_or_signal, string)));
+let check_string = Alcotest.(check(string));
+let check_bool = Alcotest.(check(bool));
+let check_get_args =
+  Alcotest.(
+    check(
+      Alcotest.result(Alcotest.triple(string, string, list(string)), unit),
+    )
+  );
+
+let test_run_process_success = () =>
+  check_exit_or_signal(
+    "Returns expected",
+    (Ok(), ""),
+    run_process("true", []),
+  );
+
+let test_run_process_failure = () =>
+  check_exit_or_signal(
+    "Returns expected",
+    (Error(`Exit_non_zero(1)), ""),
+    run_process("false", []),
+  );
+
+let test_run_process_stdout = () =>
+  check_exit_or_signal(
+    "Returns expected",
+    (Ok(), "echoed\n"),
+    run_process("echo", ["echoed"]),
+  );
+
+let test_hash_one = () => {
+  check_string(
+    "Hash matches",
+    hash_files([|"../LICENSE"|]),
+    "b43cf2e824eb66ba0e8f939c08072a8e307b5e5f",
+  );
+};
+
+let test_hash_multiple = () => {
+  check_string(
+    "Hash matches",
+    hash_files([|"../LICENSE", "../LICENSE"|]),
+    "08304d8baeed02722f81252952b00f6ac011ce0c",
+  );
+};
+
+let test_hash_filters_nonexistent = () => {
+  check_string(
+    "Hash matches",
+    hash_files([|"../LICENSE", "FOOBARBAZ"|]),
+    "b43cf2e824eb66ba0e8f939c08072a8e307b5e5f",
+  );
+};
+
+let test_rmrf_file = () => {
+  let tmp_file_name = Filename_unix.temp_file("test", "txt");
+  rmrf(tmp_file_name);
+
+  check_bool(
+    "File removed",
+    false,
+    _syst_to_bool(Sys_unix.is_file(tmp_file_name)),
+  );
+};
+
+let test_rmrf_dir = () => {
+  let temp_dir_name = Filename_unix.temp_dir("test", "d");
+  let _ = Filename_unix.temp_file(~in_dir=temp_dir_name, "test", "txt");
+
+  rmrf(temp_dir_name);
+
+  check_bool(
+    "File removed",
+    false,
+    _syst_to_bool(Sys_unix.file_exists(temp_dir_name)),
+  );
+};
+
+let test_get_args_simple = () => {
+  check_get_args(
+    "Parses successfully",
+    Ok(("foo", "bar", ["oof", "rab", "zab"])),
+    get_args([|"000", "foo", "bar", "oof", "rab", "zab"|]),
+  );
+};
+
+let test_get_args_just_enough = () => {
+  check_get_args(
+    "Parses just enough args",
+    Ok(("foo", "bar", [])),
+    get_args([|"000", "foo", "bar"|]),
+  );
+};
+
+let test_get_args_error = () => {
+  check_get_args("Errors on too few args", Error(), get_args([|"000", "111"|]))
+};
+
+let () =
+  Alcotest.(
+    run(
+      "Watches",
+      [
+        (
+          "run_process",
+          [
+            test_case("Capture's Stdout", `Quick, test_run_process_stdout),
+            test_case("Success", `Quick, test_run_process_success),
+            test_case("Failure", `Quick, test_run_process_failure),
+          ],
+        ),
+        (
+          "hash_files",
+          [
+            test_case("Hashes one file", `Quick, test_hash_one),
+            test_case("Hashes multiple files", `Quick, test_hash_multiple),
+            test_case(
+              "Filters non-existent",
+              `Quick,
+              test_hash_filters_nonexistent,
+            ),
+          ],
+        ),
+        (
+          "rmrf helper",
+          [
+            test_case("Removes file", `Quick, test_rmrf_file),
+            test_case("Removes dir", `Quick, test_rmrf_dir),
+          ],
+        ),
+        (
+          "get_args",
+        [
+          test_case("Parses Args", `Quick, test_get_args_simple),
+          test_case("Parses just enough args", `Quick, test_get_args_just_enough),
+          test_case("Handles too few args", `Quick, test_get_args_error)
+        ],
+        ),
+      ],
+    )
+  );
diff --git a/tests/flake_env_test_versions.re b/tests/flake_env_test_versions.re
new file mode 100644
index 0000000..5b06a48
--- /dev/null
+++ b/tests/flake_env_test_versions.re
@@ -0,0 +1,174 @@
+open Lib;
+
+let pprint = (pp_fmt, version) => {
+  Versions.(
+    Fmt.pf(
+      pp_fmt,
+      "{ major: %d, minor: %d, point: %d }",
+      version.major,
+      version.minor,
+      version.point,
+    )
+  );
+};
+let testable_version =
+  Alcotest.testable(pprint, (a, b) => Versions.compare(a, b) == 0);
+
+let check_version =
+  Alcotest.(check(Alcotest.result(testable_version, string)));
+
+let test_compare_equal = () => {
+  let a = Versions.init(1, 0, 0);
+  Alcotest.(check(int))("equal", 0, Versions.compare(a, a));
+};
+
+let test_compare_first_major_greater = () => {
+  let a = Versions.init(2, 0, 0);
+  let b = Versions.init(1, 0, 0);
+  Alcotest.(check(int))("First major greater", 1, Versions.compare(a, b));
+};
+
+let test_compare_first_minor_greater = () => {
+  let a = Versions.init(1, 1, 0);
+  let b = Versions.init(1, 0, 0);
+  Alcotest.(check(int))("First minor greater", 1, Versions.compare(a, b));
+};
+
+let test_compare_first_point_greater = () => {
+  let a = Versions.init(1, 0, 1);
+  let b = Versions.init(1, 0, 0);
+  Alcotest.(check(int))("First point greater", 1, Versions.compare(a, b));
+};
+
+let test_compare_second_major_greater = () => {
+  let a = Versions.init(1, 0, 0);
+  let b = Versions.init(2, 0, 0);
+  Alcotest.(check(int))("Second major greater", -1, Versions.compare(a, b));
+};
+
+let test_compare_second_minor_greater = () => {
+  let a = Versions.init(1, 0, 0);
+  let b = Versions.init(1, 1, 0);
+  Alcotest.(check(int))("Second minor greater", -1, Versions.compare(a, b));
+};
+
+let test_compare_second_point_greater = () => {
+  let a = Versions.init(1, 0, 0);
+  let b = Versions.init(1, 0, 1);
+  Alcotest.(check(int))("Second point greater", -1, Versions.compare(a, b));
+};
+
+let test_ine_cur_newer = () => {
+  let a = Ok(Versions.init(2, 0, 0));
+  let b = Versions.init(1, 0, 0);
+  let ine = Versions.is_new_enough(a, b);
+  Alcotest.(check(bool))("Curr newer", true, ine |> Result.get_ok);
+};
+
+let test_ine_cur_older = () => {
+  let a = Ok(Versions.init(1, 0, 0));
+  let b = Versions.init(2, 0, 0);
+  let ine = Versions.is_new_enough(a, b);
+  Alcotest.(check(bool))("Curr older", false, ine |> Result.get_ok);
+};
+
+let test_ine_cur_equal = () => {
+  let a = Versions.init(1, 0, 0);
+  let ine = Versions.is_new_enough(Ok(a), a);
+  Alcotest.(check(bool))("Curr equal", true, ine |> Result.get_ok);
+};
+
+let test_ine_error = () => {
+  let a = Error("foobarbaz");
+  let ine = Versions.is_new_enough(a, Versions.init(1, 0, 0));
+  Alcotest.(check(Alcotest.result(bool, string)))(
+    "Error bubbled",
+    Error("foobarbaz"),
+    ine,
+  );
+};
+
+let test_in_direnv_true = () => {
+  Core_unix.putenv(~key="direnv", ~data="direnv");
+  Alcotest.(check(bool))("In direnv", true, Versions.in_direnv());
+};
+
+let test_in_direnv_false = () => {
+  Core_unix.unsetenv("direnv");
+  Alcotest.(check(bool))("Not in direnv", false, Versions.in_direnv());
+};
+
+let test_extract_version_number_success = () => {
+  let result = Versions.extract_version_number("../tests/spit_version.sh");
+  check_version("Versions", Ok(Versions.init(1, 1, 1)), result);
+};
+
+// TODO: Test:
+// * extract_version_number: impure, don't know how to get a concrete version number to test against
+// * preflight_versions? impure, but m
+let () =
+  Alcotest.(
+    run(
+      "Versions",
+      [
+        (
+          "compare",
+          [
+            test_case("Versions Equal", `Quick, test_compare_equal),
+            test_case(
+              "First Major Greater",
+              `Quick,
+              test_compare_first_major_greater,
+            ),
+            test_case(
+              "First Minor Greater",
+              `Quick,
+              test_compare_first_minor_greater,
+            ),
+            test_case(
+              "First Point Greater",
+              `Quick,
+              test_compare_first_point_greater,
+            ),
+            test_case(
+              "Second Major Greater",
+              `Quick,
+              test_compare_second_major_greater,
+            ),
+            test_case(
+              "Second Minor Greater",
+              `Quick,
+              test_compare_second_minor_greater,
+            ),
+            test_case(
+              "Second Point Greater",
+              `Quick,
+              test_compare_second_point_greater,
+            ),
+          ],
+        ),
+        (
+          "is_new_enough",
+          [
+            test_case("Curr Newer", `Quick, test_ine_cur_newer),
+            test_case("Curr Older", `Quick, test_ine_cur_older),
+            test_case("Curr Equal", `Quick, test_ine_cur_equal),
+            test_case("Error", `Quick, test_ine_error),
+          ],
+        ),
+        (
+          "in_direnv",
+          [
+            test_case("true", `Quick, test_in_direnv_true),
+            test_case("false", `Quick, test_in_direnv_false),
+          ],
+        ),
+        (
+          "extract_version_number",
+          [
+            test_case("success", `Quick, test_extract_version_number_success),
+          ],
+        ),
+      ],
+    )
+  );
diff --git a/tests/flake_env_test_watches.re b/tests/flake_env_test_watches.re
new file mode 100644
index 0000000..38d4226
--- /dev/null
+++ b/tests/flake_env_test_watches.re
@@ -0,0 +1,41 @@
+open Lib.Watches;
+
+let test_get_path_removes_prefix = () => {
+  let input = `Assoc([
+    ("path", `String("aaaaaaaaaaabbbbb"))
+  ]);
+  Alcotest.(check(string))("Prefix removed", "bbbbb", get_path(input))
+};
+
+let test_get_paths_from_doc = () => {
+  let input = `Assoc([
+    ("path", `String("aaaaaaaaaaabbbbb")),
+    ("inputs", `Assoc([
+    ("foo", `Assoc([
+      ("path", `String("aaaaaaaaaaaccccc")),
+      ("inputs", `Assoc([
+      ("bar", `Assoc([
+        ("path", `String("aaaaaaaaaaaddddd")),
+        ("inputs", `Assoc([]))
+      ]))
+    ]))
+    ]))
+  ]))
+  ]);
+  Alcotest.(check(list(string)))("Gathers all inputs", ["bbbbb", "ccccc", "ddddd"], get_paths_from_doc(input, []))
+};
+
+let () =
+  Alcotest.(
+  run(
+    "Watches",
+    [("get_path",
+      [
+      test_case("Removes prefix", `Quick, test_get_path_removes_prefix),
+    ]),
+     ("get_paths_from_doc",
+      [
+       test_case("Collects all paths", `Quick, test_get_paths_from_doc),
+     ])
+  ]),
+);
diff --git a/tests/spit_version.sh b/tests/spit_version.sh
new file mode 100755
index 0000000..b2eee26
--- /dev/null
+++ b/tests/spit_version.sh
@@ -0,0 +1,2 @@
+#!/usr/bin/env sh
+echo "1.1.1";