json: only attempt python & node schema conversion tests if their bins are present

Tests introduced in ggml-org#5978
disabled in ggml-org#6198

Author: ochafik

tests/test-json-schema-to-grammar.cpp

@@ -803,18 +803,28 @@ int main() {
             tc.verify_status(FAILURE);
         }
     });
-    //test_all("Python", [](const TestCase & tc) {
-    //    write("test-json-schema-input.tmp", tc.schema);
-    //    tc.verify_status(std::system(
-    //        "python ./examples/json-schema-to-grammar.py test-json-schema-input.tmp > test-grammar-output.tmp") == 0 ? SUCCESS : FAILURE);
-    //    tc.verify(read("test-grammar-output.tmp"));
-    //});
-    //test_all("JavaScript", [](const TestCase & tc) {
-    //    write("test-json-schema-input.tmp", tc.schema);
-    //    tc.verify_status(std::system(
-    //        "node ./tests/run-json-schema-to-grammar.mjs test-json-schema-input.tmp > test-grammar-output.tmp") == 0 ? SUCCESS : FAILURE);
-    //    tc.verify(read("test-grammar-output.tmp"));
-    //});
+
+    if (std::system("python --version") == 0) {
+        test_all("Python", [](const TestCase & tc) {
+            write("test-json-schema-input.tmp", tc.schema);
+            tc.verify_status(std::system(
+                "python ./examples/json-schema-to-grammar.py test-json-schema-input.tmp > test-grammar-output.tmp") == 0 ? SUCCESS : FAILURE);
+            tc.verify(read("test-grammar-output.tmp"));
+        });
+    } else {
+        fprintf(stderr, "#\n# WARNING: Python not found, skipping Python JSON schema -> grammar tests!\n#\n");
+    }
+
+    if (std::system("node --version") == 0) {
+        test_all("JavaScript", [](const TestCase & tc) {
+            write("test-json-schema-input.tmp", tc.schema);
+            tc.verify_status(std::system(
+                "node ./tests/run-json-schema-to-grammar.mjs test-json-schema-input.tmp > test-grammar-output.tmp") == 0 ? SUCCESS : FAILURE);
+            tc.verify(read("test-grammar-output.tmp"));
+        });
+    } else {
+        fprintf(stderr, "#\n# WARNING: Node not found, skipping JavaScript JSON schema -> grammar tests!\n#\n");
+    }
 
     test_all("Check Expectations Validity", [](const TestCase & tc) {
         if (tc.expected_status == SUCCESS) {