From 5c73fbbe339753bc1838d7e401af14828b8fc070 Mon Sep 17 00:00:00 2001
From: Andrei Picus <NiGhTTraX@users.noreply.github.com>
Date: Mon, 12 Jun 2023 20:54:42 +0200
Subject: [PATCH] feat: Improve `isString` diff

---
 src/expectation/it.ts           | 44 ++++++++++++++++++++++++++++++---
 src/expectation/matcher.spec.ts | 43 ++++++++++++++++++++++++++++++--
 2 files changed, 81 insertions(+), 6 deletions(-)

diff --git a/src/expectation/it.ts b/src/expectation/it.ts
index 0678864..335c0ab 100644
--- a/src/expectation/it.ts
+++ b/src/expectation/it.ts
@@ -197,10 +197,46 @@ const isString = ({
       return matching?.test(actual) ?? true;
     },
     {
-      toJSON: () =>
-        containing || matching
-          ? `string(${printExpected(containing || matching)})`
-          : 'string',
+      toJSON: () => {
+        if (containing) {
+          return `string('${containing}')`;
+        }
+
+        if (matching) {
+          return `string(${matching})`;
+        }
+
+        return 'string';
+      },
+      getDiff: (actual) => {
+        if (typeof actual !== 'string') {
+          return {
+            expected: 'string',
+            actual: `${actual} (${typeof actual})`,
+          };
+        }
+
+        if (containing) {
+          if (actual.indexOf(containing) === -1) {
+            return {
+              expected: `string containing '${containing}'`,
+              actual,
+            };
+          }
+        }
+
+        if (matching) {
+          if (!matching.test(actual)) {
+            return {
+              expected: `string matching ${matching}`,
+              actual,
+            };
+          }
+        }
+
+        // Return the actual value twice to get a 0-diff.
+        return { expected: actual, actual };
+      },
     }
   );
 };
diff --git a/src/expectation/matcher.spec.ts b/src/expectation/matcher.spec.ts
index c39281f..dbd0b41 100644
--- a/src/expectation/matcher.spec.ts
+++ b/src/expectation/matcher.spec.ts
@@ -1,5 +1,5 @@
-import { It } from './it';
 import { expectAnsilessEqual } from '../../tests/ansiless';
+import { It } from './it';
 
 describe('It', () => {
   describe('deepEquals', () => {
@@ -423,13 +423,52 @@ describe('It', () => {
       expectAnsilessEqual(It.isString().toJSON(), 'string');
       expectAnsilessEqual(
         It.isString({ containing: 'foo' }).toJSON(),
-        'string("foo")'
+        "string('foo')"
       );
       expectAnsilessEqual(
         It.isString({ matching: /bar/ }).toJSON(),
         'string(/bar/)'
       );
     });
+
+    it("should print diff when there's a match", () => {
+      expect(It.isString().getDiff('foo')).toEqual({
+        actual: 'foo',
+        expected: 'foo',
+      });
+
+      expect(It.isString({ containing: 'foo' }).getDiff('foobar')).toEqual({
+        actual: 'foobar',
+        expected: 'foobar',
+      });
+
+      expect(It.isString({ matching: /foo/ }).getDiff('foobar')).toEqual({
+        actual: 'foobar',
+        expected: 'foobar',
+      });
+    });
+
+    it("should print diff when there's a mismatch", () => {
+      expect(It.isString().getDiff(42)).toEqual({
+        actual: '42 (number)',
+        expected: 'string',
+      });
+
+      expect(It.isString({ containing: 'foo' }).getDiff(42)).toEqual({
+        actual: '42 (number)',
+        expected: 'string',
+      });
+
+      expect(It.isString({ containing: 'foo' }).getDiff('bar')).toEqual({
+        actual: 'bar',
+        expected: "string containing 'foo'",
+      });
+
+      expect(It.isString({ matching: /foo/ }).getDiff('bar')).toEqual({
+        actual: 'bar',
+        expected: 'string matching /foo/',
+      });
+    });
   });
 
   describe('isArray', () => {