test(packages/stdlib): trigram distance tests

packages/stdlib/src/text/index.ts

@@ -1 +1,2 @@
 export * from './levenshtein-distance';
+export * from './trigram-distance';

packages/stdlib/src/text/trigram-distance/index.test.ts

@@ -0,0 +1,93 @@
+import { describe, it, expect } from 'vitest';
+import { trigramDistance, trigramProfile } from '.';
+
+describe('trigramProfile', () => {
+    it('trigram profile of a text with different trigrams', () => {
+        const different_trigrams = 'hello world';
+        const profile1 = trigramProfile(different_trigrams);
+
+        expect(profile1).toEqual(new Map([
+            ['\n\nh', 1],
+            ['\nhe', 1],
+            ['hel', 1],
+            ['ell', 1],
+            ['llo', 1],
+            ['lo ', 1],
+            ['o w', 1],
+            [' wo', 1],
+            ['wor', 1],
+            ['orl', 1],
+            ['rld', 1],
+            ['ld\n', 1],
+            ['d\n\n', 1]
+        ]));
+    });
+
+    it('trigram profile of a text with repeated trigrams', () => {
+        const repeated_trigrams = 'hello hello';
+        const profile2 = trigramProfile(repeated_trigrams);
+
+        expect(profile2).toEqual(new Map([
+            ['\n\nh', 1],
+            ['\nhe', 1],
+            ['hel', 2],
+            ['ell', 2],
+            ['llo', 2],
+            ['lo ', 1],
+            ['o h', 1],
+            [' he', 1],
+            ['lo\n', 1],
+            ['o\n\n', 1]
+        ]));
+    });
+
+    it('trigram profile of an empty text', () => {
+        const text = '';
+        const profile = trigramProfile(text);
+
+        expect(profile).toEqual(new Map([
+            ['\n\n\n', 2],
+        ]));
+    });
+});
+
+describe('trigramDistance', () => {
+    it('zero when comparing the same text', () => {
+        const profile1 = trigramProfile('hello world');
+        const profile2 = trigramProfile('hello world');
+
+        expect(trigramDistance(profile1, profile2)).toBe(0);
+    });
+
+    it('one for completely different text', () => {
+        const profile1 = trigramProfile('hello world');
+        const profile2 = trigramProfile('lorem ipsum');
+
+        expect(trigramDistance(profile1, profile2)).toBe(1);
+    });
+
+    it('one for empty text and non-empty text', () => {
+        const profile1 = trigramProfile('hello world');
+        const profile2 = trigramProfile('');
+
+        expect(trigramDistance(profile1, profile2)).toBe(1);
+    });
+
+    it('approximately 0.5 for similar text', () => {
+        const profile1 = trigramProfile('hello world');
+        const profile2 = trigramProfile('hello lorem');
+
+        const approx = trigramDistance(profile1, profile2);
+
+        expect(approx).toBeGreaterThan(0.45);
+        expect(approx).toBeLessThan(0.55);
+    });
+
+    it('triangle inequality', () => {
+        const A = trigramDistance(trigramProfile('metric'), trigramProfile('123ric'));
+        const B = trigramDistance(trigramProfile('123ric'), trigramProfile('123456'));
+        const C = trigramDistance(trigramProfile('metric'), trigramProfile('123456'));
+
+        expect(A + B).toBeGreaterThanOrEqual(C);
+    });
+});