test: add unit tests

src/utils/latin.ts

@@ -1,3 +1,5 @@
+/* eslint-disable prefer-spread */
+
 /**
  * This function is an optimization for small basic latin strings.
  * @internal
@@ -57,7 +59,6 @@ export function tryLatin(uint8array: Uint8Array, start: number, end: number): st
     }
 
     if (basicLatin) {
-      // eslint-disable-next-line prefer-spread
       return String.fromCharCode.apply(String, latinBytes);
     }
   }

test/node/utils/latin.test.ts

@@ -0,0 +1,118 @@
+import { expect } from 'chai';
+import { tryLatin } from '../../../src/utils/latin';
+import * as sinon from 'sinon';
+
+describe('tryLatin()', () => {
+  context('when given a buffer of length 0', () => {
+    it('returns an empty string', () => {
+      expect(tryLatin(new Uint8Array(), 0, 10)).to.equal('');
+    });
+  });
+
+  context('when the distance between end and start is 0', () => {
+    it('returns an empty string', () => {
+      expect(tryLatin(new Uint8Array([1, 2, 3]), 0, 0)).to.equal('');
+    });
+  });
+
+  let pushSpy;
+  let fromCharCodeSpy;
+
+  beforeEach(() => {
+    pushSpy = sinon.spy(Array.prototype, 'push');
+    fromCharCodeSpy = sinon.spy(String, 'fromCharCode');
+  });
+
+  afterEach(() => {
+    sinon.restore();
+  });
+
+  context('when there is 1 byte', () => {
+    context('that exceed 127', () => {
+      it('returns null', () => {
+        expect(tryLatin(new Uint8Array([128]), 0, 1)).be.null;
+      });
+    });
+
+    it('calls fromCharCode once', () => {
+      tryLatin(new Uint8Array([95]), 0, 1);
+      expect(fromCharCodeSpy).to.have.been.calledOnce;
+    });
+
+    it('never calls array.push', () => {
+      tryLatin(new Uint8Array([95]), 0, 1);
+      expect(pushSpy).to.have.not.been.called;
+    });
+  });
+
+  context('when there is 2 bytes', () => {
+    context('that exceed 127', () => {
+      it('returns null', () => {
+        expect(tryLatin(new Uint8Array([0, 128]), 0, 2)).be.null;
+        expect(tryLatin(new Uint8Array([128, 0]), 0, 2)).be.null;
+        expect(tryLatin(new Uint8Array([128, 128]), 0, 2)).be.null;
+      });
+    });
+
+    it('calls fromCharCode twice', () => {
+      tryLatin(new Uint8Array([95, 105]), 0, 2);
+      expect(fromCharCodeSpy).to.have.been.calledTwice;
+    });
+
+    it('never calls array.push', () => {
+      tryLatin(new Uint8Array([95, 105]), 0, 2);
+      expect(pushSpy).to.have.not.been.called;
+    });
+  });
+
+  context('when there is 3 bytes', () => {
+    context('that exceed 127', () => {
+      it('returns null', () => {
+        expect(tryLatin(new Uint8Array([0, 0, 128]), 0, 3)).be.null;
+        expect(tryLatin(new Uint8Array([0, 128, 0]), 0, 3)).be.null;
+        expect(tryLatin(new Uint8Array([128, 0, 0]), 0, 3)).be.null;
+        expect(tryLatin(new Uint8Array([128, 128, 128]), 0, 3)).be.null;
+        expect(tryLatin(new Uint8Array([128, 128, 0]), 0, 3)).be.null;
+        expect(tryLatin(new Uint8Array([128, 0, 128]), 0, 3)).be.null;
+        expect(tryLatin(new Uint8Array([0, 128, 128]), 0, 3)).be.null;
+      });
+    });
+
+    it('calls fromCharCode thrice', () => {
+      tryLatin(new Uint8Array([95, 105, 100]), 0, 3);
+      expect(fromCharCodeSpy).to.have.been.calledThrice;
+    });
+
+    it('never calls array.push', () => {
+      tryLatin(new Uint8Array([95, 105, 100]), 0, 3);
+      expect(pushSpy).to.have.not.been.called;
+    });
+  });
+
+  for (let stringLength = 4; stringLength <= 20; stringLength++) {
+    context(`when there is ${stringLength} bytes`, () => {
+      context('that exceed 127', () => {
+        it('returns null', () => {
+          expect(tryLatin(new Uint8Array(stringLength).fill(128), 0, stringLength)).be.null;
+        });
+      });
+
+      it('calls fromCharCode once', () => {
+        tryLatin(new Uint8Array(stringLength).fill(95), 0, stringLength);
+        expect(fromCharCodeSpy).to.have.been.calledOnce;
+      });
+
+      it(`calls array.push ${stringLength}`, () => {
+        tryLatin(new Uint8Array(stringLength).fill(95), 0, stringLength);
+        expect(pushSpy).to.have.callCount(stringLength);
+      });
+    });
+  }
+
+  context('when there is >21 bytes', () => {
+    it('returns null', () => {
+      expect(tryLatin(new Uint8Array(21).fill(95), 0, 21)).be.null;
+      expect(tryLatin(new Uint8Array(201).fill(95), 0, 201)).be.null;
+    });
+  });
+});