Nullable expressions: undefined -> null (#2)

- Changes expressions to use the `null` data type instead of `undefined`.
- This change caused some issues with the type snapshot checks.  Refactored the test snapshots to use `jest-runner-tsd`.  These tests now can check on the actual result set data type, rather than having to use the `GetDataType` class to extract nullability.
- Refactors the result set types to reduce duplication, and better explain that the `GetDataType` helper is now only used in `FromItemQuery`, rather than for testing only.
- Modifies the `toSql` helper to accept `Tokenable` types.

README.md

@@ -2,7 +2,8 @@ This is a fork of [@ff00ff/mammoth](https://github.com/Ff00ff/mammoth).  We made
 
 This fork is based on the 1.x version rather than newer 2.x version.  We made this decision because the 2.x version is still in alpha, and we ran into memory issues during TS compilation in the probject we were using it for.  We start from [c7c525c978aa6326042b35ca95f93699a69370c5](https://github.com/Anrok/mammoth/commit/c7c525c978aa6326042b35ca95f93699a69370c5) because that is the last commit before the big 2.x refactor.
 
-[List of changes](https://github.com/Anrok/mammoth/compare/main...c7c525c978aa6326042b35ca95f93699a69370c5)
+### List of changes ([commits](https://github.com/Anrok/mammoth/compare/main...c7c525c978aa6326042b35ca95f93699a69370c5))
+- Changes nullable expressions to use the `null` data type, rather than `undefined`.
 
 ---
 

package.json

@@ -18,10 +18,11 @@
     ".build"
   ],
   "devDependencies": {
+    "@tsd/typescript": "^5.2.2",
     "@types/jest": "^26.0.24",
     "@types/node": "^16.4.10",
-    "dts-jest": "^23.3.0",
     "jest": "^26.6.3",
+    "jest-runner-tsd": "^6.0.0",
     "prettier": "^3.0.3",
     "ts-jest": "^26.5.6",
     "typescript": "^4.3.5"
@@ -35,23 +36,38 @@
     "prepublishOnly": "npm run build && npm test"
   },
   "jest": {
-    "moduleFileExtensions": [
-      "ts",
-      "js"
-    ],
-    "coveragePathIgnorePatterns": [
-      "__tests__",
-      "__checks__"
-    ],
-    "testPathIgnorePatterns": [
-      "/\\.build/",
-      "/node_modules/",
-      "helpers"
-    ],
-    "testRegex": "/__tests__|__checks__/.*\\.(test|check)\\.ts$",
-    "transform": {
-      "\\.check\\.ts$": "dts-jest/transform",
-      "\\.ts$": "ts-jest"
-    }
+    "projects": [
+      {
+        "displayName": "unit",
+        "moduleFileExtensions": [
+          "ts",
+          "js"
+        ],
+        "coveragePathIgnorePatterns": [
+          "__tests__",
+          "__checks__"
+        ],
+        "testPathIgnorePatterns": [
+          "/\\.build/",
+          "/node_modules/",
+          "helpers"
+        ],
+        "testMatch": ["**/__tests__/*.test.ts"],
+        "transform": {
+          "\\.ts$": "ts-jest"
+        },
+        "reporters": [
+          "default"
+        ]
+      },
+      {
+        "displayName": {
+            "color": "blue",
+            "name": "types"
+        },
+        "runner": "jest-runner-tsd",
+        "testMatch": ["**/__checks__/*.check.ts"]
+      }
+    ]
   }
 }