fix: check for kubeconfig path + kubectl exec before enabling mode

Closes #158.

docs/references/changelog.md

@@ -11,6 +11,11 @@ versioning][semver].
 
 ## Unreleased
 
+### Fixed
+
+- Fixed a bug where `kele-mode` errors out when the kubeconfig file does not
+  exist yet
+
 ### Changed
 
 - Bumped dependency `plz` from `0.3` to `0.4`

kele.el

@@ -1198,10 +1198,23 @@ Only populated if Embark is installed.")
       (dolist (entry kele--embark-keymap-entries)
         (delete entry embark-keymap-alist)))))
 
+(defun kele--precheck ()
+  "Return an error if `kele-mode' is not ready to be enabled.
+
+Ensures various preconditions are met,
+e.g. `kele-kubectl-executable' is actually present."
+
+  (when (not (executable-find kele-kubectl-executable))
+    (error "`%s' not found on PATH" kele-kubectl-executable))
+
+  (when (not (file-exists-p kele-kubeconfig-path))
+    (error "`%s' does not exist; set up kubectl properly and try again" kele-kubeconfig-path)))
+
 (defun kele--enable ()
   "Enables Kele functionality.
 
 This is idempotent."
+  (kele--precheck)
   (unless kele--enabled
     (setq kele--enabled t)
     ;; FIXME: Update the watcher when `kele-kubeconfig-path' changes.

tests/unit/test-kele.el

@@ -530,7 +530,23 @@ metadata:
       (it "does nothing"
         (kele-mode 1)
         (expect 'kele--cache-start :not :to-have-been-called)
-        (expect 'kele--setup-embark-maybe :not :to-have-been-called))))
+        (expect 'kele--setup-embark-maybe :not :to-have-been-called)))
+    (describe "when `kele-kubectl-executable' not found"
+      (before-each
+        (spy-on 'executable-find
+                :and-call-fake
+                (lambda (exec)
+                  (not (string-equal exec kele-kubectl-executable)))))
+      (it "throws error"
+        (expect (kele-mode 1) :to-throw 'error)))
+    (describe "when `kele-kubeconfig-path' does not exist"
+      (before-each
+        (spy-on 'file-exists-p
+                :and-call-fake
+                (lambda (f)
+                  (not (string-equal f kele-kubeconfig-path)))))
+      (it "throws error"
+        (expect (kele-mode 1) :to-throw 'error))))
   (describe "disabling"
     (describe "when `kele--enabled' is nil"
       (before-each