diff --git a/package-lock.json b/package-lock.json
index 352224e43e..b5963855df 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,6 +11,7 @@
       "devDependencies": {
         "@docusaurus/core": "3.5.2",
         "@docusaurus/preset-classic": "3.5.2",
+        "@dotenvx/dotenvx": "^1.14.0",
         "@mdx-js/react": "3.0.1",
         "@svgr/webpack": "8.1.0",
         "@types/chai": "4.3.19",
@@ -3759,6 +3760,95 @@
         "node": ">=18.0"
       }
     },
+    "node_modules/@dotenvx/dotenvx": {
+      "version": "1.14.0",
+      "resolved": "https://registry.npmjs.org/@dotenvx/dotenvx/-/dotenvx-1.14.0.tgz",
+      "integrity": "sha512-ujWncblsqokvW8w6tCW35hjwlD3FHySMdrC5OPMYqfcGR96B/H6xK9xSu5F/SyZ8uk8USoPZynsXxB24IGvfmQ==",
+      "dev": true,
+      "license": "BSD-3-Clause",
+      "dependencies": {
+        "commander": "^11.1.0",
+        "dotenv": "^16.4.5",
+        "eciesjs": "^0.4.6",
+        "execa": "^5.1.1",
+        "fdir": "^6.2.0",
+        "ignore": "^5.3.0",
+        "object-treeify": "1.1.33",
+        "picomatch": "^4.0.2",
+        "which": "^4.0.0"
+      },
+      "bin": {
+        "dotenvx": "src/cli/dotenvx.js",
+        "git-dotenvx": "src/cli/dotenvx.js"
+      },
+      "funding": {
+        "url": "https://dotenvx.com"
+      }
+    },
+    "node_modules/@dotenvx/dotenvx/node_modules/commander": {
+      "version": "11.1.0",
+      "resolved": "https://registry.npmjs.org/commander/-/commander-11.1.0.tgz",
+      "integrity": "sha512-yPVavfyCcRhmorC7rWlkHn15b4wDVgVmBA7kV4QVBsF7kv/9TKJAbAXVTxvTnwP8HHKjRCJDClKbciiYS7p0DQ==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=16"
+      }
+    },
+    "node_modules/@dotenvx/dotenvx/node_modules/fdir": {
+      "version": "6.3.0",
+      "resolved": "https://registry.npmjs.org/fdir/-/fdir-6.3.0.tgz",
+      "integrity": "sha512-QOnuT+BOtivR77wYvCWHfGt9s4Pz1VIMbD463vegT5MLqNXy8rYFT/lPVEqf/bhYeT6qmqrNHhsX+rWwe3rOCQ==",
+      "dev": true,
+      "license": "MIT",
+      "peerDependencies": {
+        "picomatch": "^3 || ^4"
+      },
+      "peerDependenciesMeta": {
+        "picomatch": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/@dotenvx/dotenvx/node_modules/isexe": {
+      "version": "3.1.1",
+      "resolved": "https://registry.npmjs.org/isexe/-/isexe-3.1.1.tgz",
+      "integrity": "sha512-LpB/54B+/2J5hqQ7imZHfdU31OlgQqx7ZicVlkm9kzg9/w8GKLEcFfJl/t7DCEDueOyBAD6zCCwTO6Fzs0NoEQ==",
+      "dev": true,
+      "license": "ISC",
+      "engines": {
+        "node": ">=16"
+      }
+    },
+    "node_modules/@dotenvx/dotenvx/node_modules/picomatch": {
+      "version": "4.0.2",
+      "resolved": "https://registry.npmjs.org/picomatch/-/picomatch-4.0.2.tgz",
+      "integrity": "sha512-M7BAV6Rlcy5u+m6oPhAPFgJTzAioX/6B0DxyvDlo9l8+T3nLKbrczg2WLUyzd45L8RqfUMyGPzekbMvX2Ldkwg==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=12"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/jonschlinkert"
+      }
+    },
+    "node_modules/@dotenvx/dotenvx/node_modules/which": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/which/-/which-4.0.0.tgz",
+      "integrity": "sha512-GlaYyEb07DPxYCKhKzplCWBJtvxZcZMrL+4UkrTSJHHPyZU4mYYTv3qaOe77H7EODLSSopAUFAc6W8U4yqvscg==",
+      "dev": true,
+      "license": "ISC",
+      "dependencies": {
+        "isexe": "^3.1.1"
+      },
+      "bin": {
+        "node-which": "bin/which.js"
+      },
+      "engines": {
+        "node": "^16.13.0 || >=18.0.0"
+      }
+    },
     "node_modules/@eslint-community/eslint-utils": {
       "version": "4.4.0",
       "resolved": "https://registry.npmjs.org/@eslint-community/eslint-utils/-/eslint-utils-4.4.0.tgz",
@@ -4179,6 +4269,45 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@noble/ciphers": {
+      "version": "0.5.3",
+      "resolved": "https://registry.npmjs.org/@noble/ciphers/-/ciphers-0.5.3.tgz",
+      "integrity": "sha512-B0+6IIHiqEs3BPMT0hcRmHvEj2QHOLu+uwt+tqDDeVd0oyVzh7BPrDcPjRnV1PV/5LaknXJJQvOuRGR0zQJz+w==",
+      "dev": true,
+      "license": "MIT",
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
+    "node_modules/@noble/curves": {
+      "version": "1.6.0",
+      "resolved": "https://registry.npmjs.org/@noble/curves/-/curves-1.6.0.tgz",
+      "integrity": "sha512-TlaHRXDehJuRNR9TfZDNQ45mMEd5dwUwmicsafcIX4SsNiqnCHKjE/1alYPd/lDRVhxdhUAlv8uEhMCI5zjIJQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@noble/hashes": "1.5.0"
+      },
+      "engines": {
+        "node": "^14.21.3 || >=16"
+      },
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
+    "node_modules/@noble/hashes": {
+      "version": "1.5.0",
+      "resolved": "https://registry.npmjs.org/@noble/hashes/-/hashes-1.5.0.tgz",
+      "integrity": "sha512-1j6kQFb7QRru7eKN3ZDvRcP13rugwdxZqCjbiAVZfIJwgj2A65UmT4TgARXGlXgnRkORLTDTrO19ZErt7+QXgA==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": "^14.21.3 || >=16"
+      },
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
     "node_modules/@nodelib/fs.scandir": {
       "version": "2.1.5",
       "resolved": "https://registry.npmjs.org/@nodelib/fs.scandir/-/fs.scandir-2.1.5.tgz",
@@ -8684,6 +8813,19 @@
         "node": ">=8"
       }
     },
+    "node_modules/dotenv": {
+      "version": "16.4.5",
+      "resolved": "https://registry.npmjs.org/dotenv/-/dotenv-16.4.5.tgz",
+      "integrity": "sha512-ZmdL2rui+eB2YwhsWzjInR8LldtZHGDoQ1ugH85ppHKwpUHL7j7rN0Ti9NCnGiQbhaZ11FpR+7ao1dNsmduNUg==",
+      "dev": true,
+      "license": "BSD-2-Clause",
+      "engines": {
+        "node": ">=12"
+      },
+      "funding": {
+        "url": "https://dotenvx.com"
+      }
+    },
     "node_modules/duplexer": {
       "version": "0.1.2",
       "resolved": "https://registry.npmjs.org/duplexer/-/duplexer-0.1.2.tgz",
@@ -8698,6 +8840,21 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/eciesjs": {
+      "version": "0.4.7",
+      "resolved": "https://registry.npmjs.org/eciesjs/-/eciesjs-0.4.7.tgz",
+      "integrity": "sha512-4JQahOkBdDy27jjW4q3FJQigHlcwZXx28sCtBQkBamF2XUdcNXrInpgrr8h205MtVIS0CMHufyIKGVjtjxQ2ZA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@noble/ciphers": "^0.5.3",
+        "@noble/curves": "^1.4.0",
+        "@noble/hashes": "^1.4.0"
+      },
+      "engines": {
+        "node": ">=16.0.0"
+      }
+    },
     "node_modules/ee-first": {
       "version": "1.1.1",
       "resolved": "https://registry.npmjs.org/ee-first/-/ee-first-1.1.1.tgz",
@@ -16104,6 +16261,16 @@
         "node": ">= 0.4"
       }
     },
+    "node_modules/object-treeify": {
+      "version": "1.1.33",
+      "resolved": "https://registry.npmjs.org/object-treeify/-/object-treeify-1.1.33.tgz",
+      "integrity": "sha512-EFVjAYfzWqWsBMRHPMAXLCDIJnpMhdWAqR7xG6M6a2cs6PMFpl/+Z20w9zDW4vkxOFfddegBKq9Rehd0bxWE7A==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">= 10"
+      }
+    },
     "node_modules/object.assign": {
       "version": "4.1.5",
       "resolved": "https://registry.npmjs.org/object.assign/-/object.assign-4.1.5.tgz",
diff --git a/package.json b/package.json
index afba3d93eb..931e1db206 100644
--- a/package.json
+++ b/package.json
@@ -37,7 +37,7 @@
     "test": "npm run lint && npm run check && npm run testonly:cover && npm run prettier:check && npm run check:spelling && npm run check:integrations",
     "lint": "eslint --cache --max-warnings 0 --rulesdir resources/eslint-internal-rules/ .",
     "check": "tsc --pretty",
-    "testonly": "mocha --full-trace src/**/__tests__/**/*-test.ts",
+    "testonly": "dotenvx run --env NODE_ENV=development -- mocha --full-trace src/**/__tests__/**/*-test.ts",
     "testonly:cover": "c8 npm run testonly",
     "testonly:watch": "npm run testonly -- --watch",
     "prettier": "prettier --cache --cache-strategy metadata --write --list-different .",
@@ -56,6 +56,7 @@
   "devDependencies": {
     "@docusaurus/core": "3.5.2",
     "@docusaurus/preset-classic": "3.5.2",
+    "@dotenvx/dotenvx": "^1.14.0",
     "@mdx-js/react": "3.0.1",
     "@svgr/webpack": "8.1.0",
     "@types/chai": "4.3.19",
diff --git a/src/jsutils/instanceOf.ts b/src/jsutils/instanceOf.ts
index 562aee3e2f..5e546d1da0 100644
--- a/src/jsutils/instanceOf.ts
+++ b/src/jsutils/instanceOf.ts
@@ -1,10 +1,10 @@
 import { inspect } from './inspect.js';
 
 /* c8 ignore next 3 */
-const isProduction =
+const isDevelopment =
   globalThis.process != null &&
   // eslint-disable-next-line no-undef
-  process.env.NODE_ENV === 'production';
+  process.env.NODE_ENV === 'development';
 
 /**
  * A replacement for instanceof which includes an error warning when multi-realm
@@ -15,11 +15,8 @@ const isProduction =
 export const instanceOf: (value: unknown, constructor: Constructor) => boolean =
   /* c8 ignore next 6 */
   // FIXME: https://github.com/graphql/graphql-js/issues/2317
-  isProduction
+  isDevelopment
     ? function instanceOf(value: unknown, constructor: Constructor): boolean {
-        return value instanceof constructor;
-      }
-    : function instanceOf(value: unknown, constructor: Constructor): boolean {
         if (value instanceof constructor) {
           return true;
         }
@@ -50,6 +47,9 @@ spurious results.`,
           }
         }
         return false;
+      }
+    : function instanceOf(value: unknown, constructor: Constructor): boolean {
+        return value instanceof constructor;
       };
 
 interface Constructor extends Function {