inventory: make resolve module a clanLib function

Unclutter inventory logic

lib/resolve-module/test.nix

@@ -0,0 +1,70 @@
+# Run: nix-unit ./test-resolve-module.nix
+{
+  lib ? import <nixpkgs/lib>,
+  clanLib ? import ../default.nix { inherit lib; },
+}:
+let
+  resolveModule = clanLib.resolveModule;
+
+  fromSpec =
+    moduleSpec:
+    resolveModule {
+      inherit moduleSpec;
+      flakeInputs = {
+        self.clan.modules = {
+          foo = {
+            name = "self/foo";
+          };
+        };
+      };
+      clanCoreModules = {
+        foo = {
+          name = "clan/foo";
+        };
+        bar = {
+          name = "clan/bar";
+        };
+      };
+    };
+
+in
+{
+  test_default_clan_core = {
+    expr = fromSpec {
+      name = "foo";
+      input = null;
+    };
+    expected = {
+      name = "clan/foo";
+    };
+  };
+  test_self_module = {
+    expr = fromSpec {
+      name = "foo";
+      input = "self";
+    };
+    expected = {
+      name = "self/foo";
+    };
+  };
+  test_missing_self_module = {
+    expr = fromSpec {
+      name = "bar";
+      input = "self";
+    };
+    expectedError = {
+      type = "ThrownError";
+      msg = "flake input 'self' doesn't provide clan-module with name 'bar'";
+    };
+  };
+  test_missing_core_module = {
+    expr = fromSpec {
+      name = "nana";
+      input = null;
+    };
+    expectedError = {
+      type = "ThrownError";
+      msg = "clan-core doesn't provide clan-module with name 'nana'";
+    };
+  };
+}