refactor(odin): port check command.

cmd_check_test.odin

@@ -0,0 +1,43 @@
+package main
+
+import "core:fmt"
+import "core:testing"
+
+@(test)
+test_find_unbacked_finds_missing :: proc(t: ^testing.T) {
+    local := []string{"/a/.env", "/b/.env", "/c/.env"}
+    db := []EnvFile{{Path = "/a/.env"}, {Path = "/b/.env"}}
+
+    result := find_unbacked(local, db[:])
+    testing.expect(t, len(result) == 1, fmt.aprintf("expected 1 unbacked, got %d", len(result)))
+    if len(result) > 0 {
+        testing.expect(t, result[0] == "/c/.env", fmt.aprintf("expected /c/.env, got %s", result[0]))
+    }
+}
+
+@(test)
+test_find_unbacked_all_backed :: proc(t: ^testing.T) {
+    local := []string{"/a/.env", "/b/.env"}
+    db := []EnvFile{{Path = "/a/.env"}, {Path = "/b/.env"}}
+
+    result := find_unbacked(local, db[:])
+    testing.expect(t, len(result) == 0, fmt.aprintf("expected 0 unbacked, got %d", len(result)))
+}
+
+@(test)
+test_find_unbacked_no_local :: proc(t: ^testing.T) {
+    local: []string
+    db := []EnvFile{{Path = "/a/.env"}}
+
+    result := find_unbacked(local, db[:])
+    testing.expect(t, len(result) == 0, fmt.aprintf("expected 0 unbacked, got %d", len(result)))
+}
+
+@(test)
+test_find_unbacked_none_backed :: proc(t: ^testing.T) {
+    local := []string{"/a/.env", "/b/.env"}
+    db: []EnvFile
+
+    result := find_unbacked(local, db[:])
+    testing.expect(t, len(result) == 2, fmt.aprintf("expected 2 unbacked, got %d", len(result)))
+}