Add stack test suite.

Author: K Hudson

.gitignore

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+built
+node_modules
+.idea

package-lock.json

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+{
+  "name": "data-structures-ts",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "type": "module",
+  "scripts": {
+    "test": "jest"
+  },
+  "jest": {
+    "transform": {
+      ".(ts|tsx)": "ts-jest"
+    },
+    "testRegex": "(/__tests__/.*|\\.(test|spec))\\.(ts|tsx|js)$",
+    "moduleFileExtensions": [
+      "ts",
+      "tsx",
+      "js"
+    ]
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "typescript": "^4.2.3"
+  },
+  "devDependencies": {
+    "@types/jest": "^26.0.22",
+    "jest": "^26.6.3",
+    "ts-jest": "^26.5.4"
+  }
+}

package.json

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+export default class Node {}

src/Node.ts

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+export default class Stack {}

src/Stack.ts

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+import Stack from "../src/Stack";
+import Node from "../src/Node";
+
+test("Smoke test ...", () => {
+    expect(true).toEqual(true);
+});
+
+describe("Stack", () => {
+    let stack: Stack;
+
+    beforeEach(() => {
+        stack = new Stack();
+    })
+
+    test("should be empty on instantiation", () => {
+        expect(stack.isEmpty()).toBeTruthy()
+    });
+
+    test("push() should add a node", () => {
+        let node: Node = new Node();
+        stack.push(node);
+        expect(stack.isEmpty()).toBeFalsy();
+    });
+
+    test("count() should count its nodes", () => {
+        let node: Node = new Node();
+        stack.push(node);
+        stack.push(node);
+        expect(stack.count()).toEqual(2);
+    });
+
+    test("pop() should remove the last node added", () => {
+        let node1: Node = new Node();
+        let node2: Node = new Node();
+        stack.push(node1);
+        stack.push(node2);
+        let lastNode = stack.pop();
+        expect(lastNode).toEqual(node2);
+    });
+
+    test("peek() should return the top node", () => {
+        let node1: Node = new Node();
+        let node2: Node = new Node();
+        stack.push(node1);
+        stack.push(node2);
+        expect(stack.peek()).toEqual(node2);
+    });
+})

tests/Stack.test.ts

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+{
+  "compilerOptions": {
+    "outDir": "./built",
+    "allowJs": true,
+    "target": "es5",
+    "module": "ES2015",
+    "lib": ["es2015"],
+    "strict": true,
+    "declaration": true,
+    "sourceMap": true
+  },
+  "include": ["./src/**/*"],
+  "exclude": ["node_modules", "**/*.test.ts"]
+}