pref: increase linked-list test coverage

.travis.yml

@@ -8,7 +8,6 @@ node_js:
   - '10'
   - '11'
   - '8'
-  - '6'
 script:
   - npm run test:prod && npm run build
 after_success:

src/linked-list/__tests__/index.ts

@@ -60,17 +60,20 @@ describe('LinkedList class', () => {
   })
 
   describe('helper functions', () => {
-    it('should stringify list correctly', () => {
+    it('Method toString()', () => {
       expect(linkedList.toString()).toBe('')
 
       linkedList.append(1)
       expect(linkedList.toString()).toBe('1')
 
       linkedList.append(2).append(3)
       expect(linkedList.toString()).toBe('1,2,3')
+
+      const stringHandler = (value: any) => value;
+      expect(linkedList.toString(stringHandler)).toBe('1,2,3');
     })
 
-    it('should toArray correctly', () => {
+    it('Method toArray()', () => {
       expect(linkedList.toArray()).toEqual([])
 
       linkedList.append(1)
@@ -147,6 +150,10 @@ describe('LinkedList class', () => {
       expect(linkedList.delete).toBeInstanceOf(Function)
     })
 
+    it("should return null if the list is empty()", () => {
+      expect(linkedList.delete(1)).toBe(null);
+    })
+
     it('should delete nothing if not found value', () => {
       linkedList
         .append(1)
@@ -192,23 +199,31 @@ describe('LinkedList class', () => {
 
   describe('Method deleteHead()', () => {
     it('should delete head node and handle head & tail correctly', () => {
-      linkedList.append(1).deleteHead()
-
-      expect(linkedList.head).toBe(null)
-      expect(linkedList.tail).toBe(null)
-
       linkedList
         .append(1)
         .append(2)
         .append(3)
         .append(4)
         .append(5)
-      linkedList.deleteHead()
+      expect((linkedList.deleteHead() as Node).value).toBe(1)
       expect(linkedList.toString()).toBe('2,3,4,5')
 
       expect((linkedList.head as Node).value).toBe(2)
       expect((linkedList.tail as Node).value).toBe(5)
     })
+
+    it("should set head & tail correctly when list have only one node", () => {
+      linkedList.append(1).deleteHead()
+
+      expect(linkedList.head).toBe(null)
+      expect(linkedList.tail).toBe(null)
+    })
+
+    it("should return null if the list is empty()", () => {
+      expect(linkedList.deleteHead()).toBe(null);
+    })
+
+
   })
 
   describe('Method deleteTail()', () => {
@@ -229,6 +244,13 @@ describe('LinkedList class', () => {
       expect((linkedList.head as Node).value).toBe(1)
       expect((linkedList.tail as Node).value).toBe(4)
     })
+
+    it("should return null when list is empty", () => {
+      expect(linkedList.deleteTail()).toBe(null);
+      linkedList.append(1)
+      linkedList.append(2)
+      expect((linkedList.deleteHead() as Node).value).toBe(1);
+    })
   })
 
   describe('Method isEmpty()', () => {
@@ -250,6 +272,7 @@ describe('LinkedList class', () => {
   })
 
   describe('Method insert()', () => {
+
     it('should insert value after specified value by default', () => {
       linkedList
         .append(1)
@@ -301,5 +324,27 @@ describe('LinkedList class', () => {
       expect((linkedList.head as Node).value).toBe(1)
       expect((linkedList.tail as Node).value).toBe(3)
     })
+
+    it('should do nothing shen targetValue not in the list', () => {
+      linkedList
+        .append(1)
+        .append(2)
+        .append(3)
+      linkedList.insert(5, 4, 'before')
+
+      expect(linkedList.toString()).toBe('1,2,3')
+    })
+
+    it("should do nothing when list empty", () => {
+      linkedList.insert(5, 3)
+      expect(linkedList.toString()).toBe('')
+      expect(linkedList.head) .toBe(null)
+      expect(linkedList.tail).toBe(null)
+
+      linkedList.insert(5, 3, "before")
+      expect(linkedList.toString()).toBe('')
+      expect(linkedList.head) .toBe(null)
+      expect(linkedList.tail).toBe(null)
+    })
   })
 })

src/linked-list/index.ts

@@ -1,5 +1,9 @@
 import { Node } from './Node'
 
+const stringifyDefault = (value: any) => {
+  return `${value}`
+}
+
 export class LinkedList {
   public head: Node | null
   public tail: Node | null
@@ -76,10 +80,6 @@ export class LinkedList {
     targetValue: any,
     direction: 'before' | 'after' = 'after'
   ): LinkedList | undefined {
-    if (!value || !targetValue) {
-      return
-    }
-
     if (direction === 'after') {
       let currentNode = this.head
 
@@ -172,11 +172,11 @@ export class LinkedList {
 
     if (headNode !== null) {
       deletedNode = headNode
-      if (headNode === this.tail) {
+      if (this.head === this.tail) {
         this.head = null
         this.tail = null
       } else {
-        this.head = headNode.next ? headNode.next : null
+        this.head = headNode.next;
       }
     }
 
@@ -231,11 +231,7 @@ export class LinkedList {
     return result
   }
 
-  public toString(
-    handler: (value: any) => string = value => {
-      return `${value}`
-    }
-  ): string {
+  public toString( handler: (value: any) => string = stringifyDefault ): string {
     return this.toArray()
       .map(value => {
         return handler(value)