refactor(NODE-4815): let maybeTruncate have a default

Author: W-A-James

src/mongo_logger.ts

@@ -255,7 +255,12 @@ export type LoggableEvent =
 export interface LogConvertible extends Record<string, any> {
   toLog(): Record<string, any>;
 }
-export function maybeTruncate(ejson: string, maxDocumentLength: number): string {
+
+/** @internal */
+export function maybeTruncate(
+  ejson: string,
+  maxDocumentLength: number = DEFAULT_MAX_DOCUMENT_LENGTH
+): string {
   if (maxDocumentLength === 0) {
     return ejson;
   }

test/unit/mongo_logger.test.ts

@@ -1216,22 +1216,47 @@ describe('class MongoLogger', function () {
 });
 
 describe('maybeTruncate', function () {
-  const largeDoc = {};
+  let largeEjsonString: string;
+  let smallEjsonString: string;
   before(function () {
-    for (let i = 0; i < 1000; i++) {
+    const largeDoc = {};
+    for (let i = 0; i < DEFAULT_MAX_DOCUMENT_LENGTH; i++) {
       largeDoc[`test${i}`] = `Hello_${i}`;
     }
+    largeEjsonString = EJSON.stringify(largeDoc);
+    const smallDoc = { test: 'Hello' };
+    smallEjsonString = EJSON.stringify(smallDoc);
   });
 
   context('when maxDocumentLength = 0', function () {
     it('does not truncate document', function () {
-      const ejson = EJSON.stringify(largeDoc);
-      expect(ejson).to.equal(maybeTruncate(ejson, 0));
+      expect(maybeTruncate(largeEjsonString, 0)).to.equal(largeEjsonString);
     });
   });
 
   context('when maxDocumentLength is non-zero', function () {
-    context('when document has length greater than maxDocumentLength', function () {});
-    context('when document has length less than or equal to maxDocumentLength', function () {});
+    context('when document has length greater than maxDocumentLength', function () {
+      it('truncates ejson string to length of maxDocumentLength + 3', function () {
+        expect(maybeTruncate(largeEjsonString)).to.have.lengthOf(DEFAULT_MAX_DOCUMENT_LENGTH + 3);
+      });
+      it('ends with "..."', function () {
+        expect(maybeTruncate(largeEjsonString)).to.match(/^.*\.\.\.$/);
+      });
+    });
+
+    context('when document has length less than or equal to maxDocumentLength', function () {
+      it('does not truncate document', function () {
+        expect(maybeTruncate(smallEjsonString)).to.equal(smallEjsonString);
+      });
+      it('does not end with "..."', function () {
+        expect(maybeTruncate(smallEjsonString)).to.not.match(/^.*\.\.\./);
+      });
+
+      it('produces valid relaxed EJSON', function () {
+        expect(() => {
+          EJSON.parse(maybeTruncate(smallEjsonString));
+        }).to.not.throw();
+      });
+    });
   });
 });