Rewrote "Rat in a maze" algorithm

It's based on the previous implementation but offers a better API and is now properly testable, too

Backtracking/tests/RatInAMaze.test.js

@@ -0,0 +1,84 @@
+import { RatInAMaze } from '../RatInAMaze'
+
+describe('RatInAMaze', () => {
+  it('should fail for non-arrays', () => {
+    const values = [undefined, null, {}, 42, 'hello, world']
+
+    for (const value of values) {
+      expect(() => {new RatInAMaze(value)}).toThrow()
+    }
+  })
+
+  it('should fail for an empty array', () => {
+    expect(() => {new RatInAMaze([])}).toThrow()
+  })
+
+  it('should fail for a non-square array', () => {
+    const array = [
+      [0, 0, 0],
+      [0, 0]
+    ]
+
+    expect(() => {new RatInAMaze(array)}).toThrow()
+  })
+
+  it('should fail for arrays containing invalid values', () => {
+    const values = [[[2]], [['a']]]
+
+    for (const value of values) {
+      expect(() => {new RatInAMaze(value)}).toThrow()
+    }
+  })
+
+  it('should work for a single-cell maze', () => {
+    const maze = new RatInAMaze([[1]])
+    expect(maze.solved).toBe(true)
+    expect(maze.path).toBe('')
+  })
+
+  it('should work for a single-cell maze that can not be solved', () => {
+    const maze = new RatInAMaze([[0]])
+    expect(maze.solved).toBe(false)
+    expect(maze.path).toBe('')
+  })
+
+  it('should work for a simple 3x3 maze', () => {
+    const maze = new RatInAMaze([[1, 1, 0], [0, 1, 0], [0, 1, 1]])
+    expect(maze.solved).toBe(true)
+    expect(maze.path).toBe('RDDR')
+  })
+
+  it('should work for a simple 2x2 that can not be solved', () => {
+    const maze = new RatInAMaze([[1, 0], [0, 1]])
+    expect(maze.solved).toBe(false)
+    expect(maze.path).toBe('')
+  })
+
+  it('should work for a more complex maze', () => {
+    const maze = new RatInAMaze([
+      [1, 1, 1, 1, 1, 0, 0],
+      [0, 0, 0, 0, 1, 0, 0],
+      [1, 1, 1, 0, 1, 0, 0],
+      [1, 0, 1, 0, 1, 0, 0],
+      [1, 0, 1, 1, 1, 0, 0],
+      [1, 0, 0, 0, 0, 0, 0],
+      [1, 1, 1, 1, 1, 1, 1]
+    ])
+    expect(maze.solved).toBe(true)
+    expect(maze.path).toBe('RRRRDDDDLLUULLDDDDRRRRRR')
+  })
+
+  it('should work for a more complex maze that can not be solved', () => {
+    const maze = new RatInAMaze([
+      [1, 1, 1, 1, 1, 0, 0],
+      [0, 0, 0, 0, 1, 0, 0],
+      [1, 1, 1, 0, 1, 0, 0],
+      [1, 0, 1, 0, 1, 0, 0],
+      [1, 0, 1, 0, 1, 0, 0],
+      [1, 0, 0, 0, 0, 0, 0],
+      [1, 1, 1, 1, 1, 1, 1]
+    ])
+    expect(maze.solved).toBe(false)
+    expect(maze.path).toBe('')
+  })
+})