feat(std/testing): Add support for object assertion against object subset

std/testing/README.md

@@ -25,6 +25,8 @@ pretty-printed diff of failing assertion.
   `expected`.
 - `assertArrayContains()` - Make an assertion that `actual` array contains the
   `expected` values.
+- `assertObjectMatch()` - Make an assertion that `actual` object match
+  `expected` subset object
 - `assertThrows()` - Expects the passed `fn` to throw. If `fn` does not throw,
   this function does. Also compares any errors thrown to an optional expected
   `Error` class and checks that the error `.message` includes an optional

std/testing/asserts.ts

@@ -429,6 +429,44 @@ export function assertNotMatch(
   }
 }
 
+/**
+ * Make an assertion that `actual` object is a subset of `expected` object, deeply.
+ * If not, then throw.
+ */
+export function assertObjectMatch(
+  actual: { [key: string]: unknown },
+  expected: { [key: string]: unknown },
+): void {
+  type loose = { [key: string]: unknown };
+  const seen = new WeakMap();
+  return assertEquals(
+    (function filter(a: loose, b: loose): loose {
+      // Prevent infinite loop with circular references with same filter
+      if ((seen.has(a)) && (seen.get(a) === b)) {
+        return a;
+      }
+      seen.set(a, b);
+      // Iterate through keys present in both actual and expected
+      // and filter recursively on object references
+      const filtered = {} as loose;
+      for (
+        const [key, value] of Object.entries(a).filter(([key]) => key in b)
+      ) {
+        if (typeof value === "object") {
+          const subset = (b as loose)[key];
+          if ((typeof subset === "object") && (subset)) {
+            filtered[key] = filter(value as loose, subset as loose);
+            continue;
+          }
+        }
+        filtered[key] = value;
+      }
+      return filtered;
+    })(actual, expected),
+    expected,
+  );
+}
+
 /**
  * Forcefully throws a failed assertion
  */

std/testing/asserts_test.ts

@@ -9,6 +9,7 @@ import {
   assertNotEquals,
   assertNotMatch,
   assertNotStrictEquals,
+  assertObjectMatch,
   assertStrictEquals,
   assertStringContains,
   assertThrows,
@@ -259,6 +260,160 @@ Deno.test("testingAssertStringNotMatchingThrows", function (): void {
   assert(didThrow);
 });
 
+Deno.test("testingAssertObjectMatching", function (): void {
+  const a = { foo: true, bar: false };
+  const b = { ...a, baz: a };
+  const c = { ...b, qux: b };
+  const d = { corge: c, grault: c };
+  const e = { foo: true } as { [key: string]: unknown };
+  e.bar = e;
+  // Simple subset
+  assertObjectMatch(a, {
+    foo: true,
+  });
+  // Subset with another subset
+  assertObjectMatch(b, {
+    foo: true,
+    baz: { bar: false },
+  });
+  // Subset with multiple subsets
+  assertObjectMatch(c, {
+    foo: true,
+    baz: { bar: false },
+    qux: {
+      baz: { foo: true },
+    },
+  });
+  // Subset with same object reference as subset
+  assertObjectMatch(d, {
+    corge: {
+      foo: true,
+      qux: { bar: false },
+    },
+    grault: {
+      bar: false,
+      qux: { foo: true },
+    },
+  });
+  // Subset with circular reference
+  assertObjectMatch(e, {
+    foo: true,
+    bar: {
+      bar: {
+        bar: {
+          foo: true,
+        },
+      },
+    },
+  });
+  // Missing key
+  {
+    let didThrow;
+    try {
+      assertObjectMatch({
+        foo: true,
+      }, {
+        foo: true,
+        bar: false,
+      });
+      didThrow = false;
+    } catch (e) {
+      assert(e instanceof AssertionError);
+      didThrow = true;
+    }
+    assertEquals(didThrow, true);
+  }
+  // Simple subset
+  {
+    let didThrow;
+    try {
+      assertObjectMatch(a, {
+        foo: false,
+      });
+      didThrow = false;
+    } catch (e) {
+      assert(e instanceof AssertionError);
+      didThrow = true;
+    }
+    assertEquals(didThrow, true);
+  }
+  // Subset with another subset
+  {
+    let didThrow;
+    try {
+      assertObjectMatch(b, {
+        foo: true,
+        baz: { bar: true },
+      });
+      didThrow = false;
+    } catch (e) {
+      assert(e instanceof AssertionError);
+      didThrow = true;
+    }
+    assertEquals(didThrow, true);
+  }
+  // Subset with multiple subsets
+  {
+    let didThrow;
+    try {
+      assertObjectMatch(c, {
+        foo: true,
+        baz: { bar: false },
+        qux: {
+          baz: { foo: false },
+        },
+      });
+      didThrow = false;
+    } catch (e) {
+      assert(e instanceof AssertionError);
+      didThrow = true;
+    }
+    assertEquals(didThrow, true);
+  }
+  // Subset with same object reference as subset
+  {
+    let didThrow;
+    try {
+      assertObjectMatch(d, {
+        corge: {
+          foo: true,
+          qux: { bar: true },
+        },
+        grault: {
+          bar: false,
+          qux: { foo: false },
+        },
+      });
+      didThrow = false;
+    } catch (e) {
+      assert(e instanceof AssertionError);
+      didThrow = true;
+    }
+    assertEquals(didThrow, true);
+  }
+  // Subset with circular reference
+  {
+    let didThrow;
+    try {
+      assertObjectMatch(e, {
+        foo: true,
+        bar: {
+          bar: {
+            bar: {
+              foo: false,
+            },
+          },
+        },
+      });
+      didThrow = false;
+    } catch (e) {
+      assert(e instanceof AssertionError);
+      didThrow = true;
+    }
+    assertEquals(didThrow, true);
+  }
+});
+
 Deno.test("testingAssertsUnimplemented", function (): void {
   let didThrow = false;
   try {