diff --git a/core/test/config/config-helpers-test.js b/core/test/config/config-helpers-test.js
index be92027d20eb..b9fc86f71237 100644
--- a/core/test/config/config-helpers-test.js
+++ b/core/test/config/config-helpers-test.js
@@ -274,6 +274,28 @@ describe('.resolveSettings', () => {
     expect(settings).not.toHaveProperty('nonsense');
   });
 
+  describe('sets UA string', () => {
+    it('to default value if provided value is undefined', () => {
+      const settings = resolveSettings({}, {emulatedUserAgent: undefined});
+      expect(settings.emulatedUserAgent).toMatch(/^Mozilla\/5.*moto.*Chrome/);
+    });
+
+    it('to default value if provided value is true', () => {
+      const settings = resolveSettings({}, {emulatedUserAgent: true});
+      expect(settings.emulatedUserAgent).toMatch(/^Mozilla\/5.*moto.*Chrome/);
+    });
+
+    it('to false if provided value is false', () => {
+      const settings = resolveSettings({}, {emulatedUserAgent: false});
+      expect(settings.emulatedUserAgent).toEqual(false);
+    });
+
+    it('to the provided string value if present', () => {
+      const settings = resolveSettings({}, {emulatedUserAgent: 'Random UA'});
+      expect(settings.emulatedUserAgent).toEqual('Random UA');
+    });
+  });
+
   describe('budgets', () => {
     it('initializes budgets', () => {
       const settings = resolveSettings({
@@ -341,7 +363,7 @@ describe('.resolveSettings', () => {
 describe('.resolveGathererToDefn', () => {
   const coreList = Runner.getGathererList();
 
-  it('should expand gatherer path short-hand', async () => {
+  it('should expand core gatherer', async () => {
     const result = await resolveGathererToDefn('image-elements', coreList);
     expect(result).toEqual({
       path: 'image-elements',
@@ -350,6 +372,15 @@ describe('.resolveGathererToDefn', () => {
     });
   });
 
+  it('should expand gatherer path short-hand', async () => {
+    const result = await resolveGathererToDefn({path: 'image-elements'}, coreList);
+    expect(result).toEqual({
+      path: 'image-elements',
+      implementation: ImageElementsGatherer,
+      instance: expect.any(ImageElementsGatherer),
+    });
+  });
+
   it('should find relative to configDir', async () => {
     const configDir = path.resolve(moduleDir, '../../gather/');
     const result = await resolveGathererToDefn('gatherers/image-elements', [], configDir);
@@ -360,6 +391,19 @@ describe('.resolveGathererToDefn', () => {
     });
   });
 
+  it('should find custom gatherers', async () => {
+    const result1 =
+      await resolveGathererToDefn('../fixtures/valid-custom-gatherer', [], moduleDir);
+    const result2 =
+      await resolveGathererToDefn('../fixtures/valid-custom-gatherer.js', [], moduleDir);
+    const result3 =
+      await resolveGathererToDefn('../fixtures/valid-custom-gatherer.cjs', [], moduleDir);
+
+    expect(result1).toMatchObject({path: '../fixtures/valid-custom-gatherer'});
+    expect(result2).toMatchObject({path: '../fixtures/valid-custom-gatherer.js'});
+    expect(result3).toMatchObject({path: '../fixtures/valid-custom-gatherer.cjs'});
+  });
+
   it('should expand gatherer impl short-hand', async () => {
     const result = await resolveGathererToDefn({implementation: ImageElementsGatherer}, coreList);
     expect(result).toEqual({
@@ -368,18 +412,60 @@ describe('.resolveGathererToDefn', () => {
     });
   });
 
+  it('should expand gatherer instance short-hand', async () => {
+    const result = await resolveGathererToDefn({instance: new ImageElementsGatherer()}, coreList);
+    expect(result).toEqual({
+      instance: expect.any(ImageElementsGatherer),
+    });
+  });
+
+  it('should expand gatherer instance directly', async () => {
+    const result = await resolveGathererToDefn(new ImageElementsGatherer(), coreList);
+    expect(result).toEqual({
+      instance: expect.any(ImageElementsGatherer),
+    });
+  });
+
   it('throws for invalid gathererDefn', async () => {
     await expect(resolveGathererToDefn({})).rejects.toThrow(/Invalid Gatherer type/);
   });
+
+  it('throws for invalid path type', async () => {
+    await expect(resolveGathererToDefn({path: 1234})).rejects.toThrow(/Invalid Gatherer type/);
+  });
+
+  it('throws but not for missing gatherer when it has a node dependency error', async () => {
+    const resultPromise =
+      resolveGathererToDefn('../fixtures/invalid-gatherers/require-error.js', [], moduleDir);
+    await expect(resultPromise).rejects.toThrow(/Cannot find module/);
+  });
 });
 
 describe('.resolveAuditsToDefns', () => {
-  it('should expand audit short-hand', async () => {
+  it('should expand core audit', async () => {
     const result = await resolveAuditsToDefns(['user-timings']);
 
     expect(result).toEqual([{path: 'user-timings', options: {}, implementation: UserTimingsAudit}]);
   });
 
+  it('should expand audit path short-hand', async () => {
+    const result = await resolveAuditsToDefns([{path: 'user-timings'}]);
+
+    expect(result).toEqual([{path: 'user-timings', options: {}, implementation: UserTimingsAudit}]);
+  });
+
+  it('should expand audit impl short-hand', async () => {
+    const result = await resolveAuditsToDefns([{implementation: UserTimingsAudit}]);
+
+    expect(result).toEqual([{options: {}, implementation: UserTimingsAudit}]);
+  });
+
+  it('should expand audit impl directly', async () => {
+    const result = await resolveAuditsToDefns([UserTimingsAudit]);
+
+    expect(result).toEqual([{options: {}, implementation: UserTimingsAudit}]);
+  });
+
   it('should find relative to configDir', async () => {
     const configDir = path.resolve(moduleDir, '../../');
     const result = await resolveAuditsToDefns(['audits/user-timings'], configDir);
@@ -389,6 +475,19 @@ describe('.resolveAuditsToDefns', () => {
     ]);
   });
 
+  it('should find custom audits', async () => {
+    const result = await resolveAuditsToDefns([
+      '../fixtures/valid-custom-audit',
+      '../fixtures/valid-custom-audit.js',
+      '../fixtures/valid-custom-audit.cjs',
+    ], moduleDir);
+    expect(result).toMatchObject([
+      {path: '../fixtures/valid-custom-audit', options: {}},
+      {path: '../fixtures/valid-custom-audit.js', options: {}},
+      {path: '../fixtures/valid-custom-audit.cjs', options: {}},
+    ]);
+  });
+
   it('should handle multiple audit definition styles', async () => {
     const result = await resolveAuditsToDefns(['user-timings', {implementation: UserTimingsAudit}]);
 
@@ -411,6 +510,13 @@ describe('.resolveAuditsToDefns', () => {
   it('throws for invalid auditDefns', async () => {
     await expect(resolveAuditsToDefns([new Gatherer()])).rejects.toThrow(/Invalid Audit type/);
   });
+
+  it('throws but not for missing audit when it has a node dependency error', async () => {
+    const resultPromise = resolveAuditsToDefns([
+      '../fixtures/invalid-audits/require-error.js',
+    ], moduleDir);
+    await expect(resultPromise).rejects.toThrow(/Cannot find module/);
+  });
 });
 
 describe('.resolveModulePath', () => {
@@ -426,6 +532,12 @@ describe('.resolveModulePath', () => {
     expect(pathToPlugin).toEqual(require.resolve(pluginName));
   });
 
+  it('throws for unknown resource', async () => {
+    expect(() => {
+      resolveModulePath('unknown', null, 'audit');
+    }).toThrow(/Unable to locate audit: `unknown`/);
+  });
+
   describe('plugin paths to a file', () => {
     it('relative to the current working directory', () => {
       const pluginName = 'lighthouse-plugin-config-helper';
diff --git a/core/test/config/config-test.js b/core/test/config/config-test.js
index 9305783b14c5..eb4fb2c0cbc3 100644
--- a/core/test/config/config-test.js
+++ b/core/test/config/config-test.js
@@ -140,6 +140,22 @@ describe('Fraggle Rock Config', () => {
     });
   });
 
+  it('is idempotent when using the resolved config as the config input', async () => {
+    const config = {
+      extends: 'lighthouse:default',
+      settings: {
+        onlyCategories: ['seo'],
+      },
+    };
+
+    const {resolvedConfig} = await initializeConfig('navigation', config);
+    expect(Object.keys(resolvedConfig.categories || {})).toEqual(['seo']);
+    expect(resolvedConfig.settings.onlyCategories).toEqual(['seo']);
+
+    const {resolvedConfig: resolvedConfig2} = await initializeConfig('navigation', resolvedConfig);
+    expect(resolvedConfig2).toEqual(resolvedConfig);
+  });
+
   describe('resolveArtifactDependencies', () => {
     /** @type {LH.Gatherer.FRGathererInstance} */
     let dependencyGatherer;
@@ -428,6 +444,12 @@ describe('Fraggle Rock Config', () => {
         expect(resolvedConfig.categories.performance.auditRefs).toContain('extra-audit');
       }
     });
+
+    it('should only accept "lighthouse:default" as the extension method', async () => {
+      extensionConfig.extends = 'something:else';
+      const resolvedConfigPromise = initializeConfig('navigation', extensionConfig);
+      await expect(resolvedConfigPromise).rejects.toThrow(/`lighthouse:default` is the only valid/);
+    });
   });
 
   it('should use failure mode fatal for the fake navigation', async () => {
diff --git a/core/test/config/filters-test.js b/core/test/config/filters-test.js
index d46ea3f05133..ebfa1ff0f797 100644
--- a/core/test/config/filters-test.js
+++ b/core/test/config/filters-test.js
@@ -25,6 +25,14 @@ describe('Fraggle Rock Config Filtering', () => {
       ...auditMeta,
     };
   }
+  class OptionalAudit extends BaseAudit {
+    static meta = {
+      id: 'optional',
+      requiredArtifacts: /** @type {any} */ (['Snapshot']),
+      __internalOptionalArtifacts: /** @type {any} */ (['Timespan']),
+      ...auditMeta,
+    };
+  }
   class ManualAudit extends BaseAudit {
     static meta = {
       id: 'manual',
@@ -230,6 +238,16 @@ describe('Fraggle Rock Config Filtering', () => {
       ]);
     });
 
+    it('should keep audits only missing optional artifacts', () => {
+      const partialArtifacts = [{id: 'Snapshot', gatherer: {instance: snapshotGatherer}}];
+      audits.push({implementation: OptionalAudit, options: {}});
+      expect(filters.filterAuditsByAvailableArtifacts(audits, partialArtifacts)).toEqual([
+        {implementation: SnapshotAudit, options: {}},
+        {implementation: ManualAudit, options: {}},
+        {implementation: OptionalAudit, options: {}},
+      ]);
+    });
+
     it('should not filter audits with dependencies on base artifacts', () => {
       class SnapshotWithBase extends BaseAudit {
         static meta = {
@@ -510,6 +528,27 @@ describe('Fraggle Rock Config Filtering', () => {
       });
     });
 
+    it('should combine category and audit filters additively', () => {
+      const filtered = filters.filterConfigByExplicitFilters(resolvedConfig, {
+        onlyCategories: ['navigation'],
+        onlyAudits: ['snapshot', 'timespan'],
+        skipAudits: [],
+      });
+      expect(filtered).toMatchObject({
+        artifacts: [{id: 'Snapshot'}, {id: 'Timespan'}],
+        audits: [
+          {implementation: SnapshotAudit},
+          {implementation: TimespanAudit},
+          {implementation: NavigationAudit},
+        ],
+        categories: {
+          navigation: {
+            auditRefs: [{id: 'navigation'}],
+          },
+        },
+      });
+    });
+
     it('should filter out audits and artifacts not in the categories by default', () => {
       resolvedConfig = {
         ...resolvedConfig,
diff --git a/core/test/config/validation-test.js b/core/test/config/validation-test.js
index 04dc8413bd42..051c4e07d0dd 100644
--- a/core/test/config/validation-test.js
+++ b/core/test/config/validation-test.js
@@ -145,6 +145,14 @@ describe('Fraggle Rock Config Validation', () => {
       expect(invocation).toThrow(/has no audit.*method/);
     });
 
+    it('should throw if audit id is missing', () => {
+      // @ts-expect-error - We are intentionally creating a malformed input.
+      ExampleAudit.meta.id = undefined;
+      const audit = {implementation: ExampleAudit, options: {}};
+      const invocation = () => validation.assertValidAudit(audit);
+      expect(invocation).toThrow(/has no meta.id/);
+    });
+
     it('should throw if title is missing', () => {
       // @ts-expect-error - We are intentionally creating a malformed input.
       ExampleAudit.meta.title = undefined;
@@ -153,6 +161,14 @@ describe('Fraggle Rock Config Validation', () => {
       expect(invocation).toThrow(/has no meta.title/);
     });
 
+    it('should throw if audit description is missing', () => {
+      // @ts-expect-error - We are intentionally creating a malformed input.
+      ExampleAudit.meta.description = undefined;
+      const audit = {implementation: ExampleAudit, options: {}};
+      const invocation = () => validation.assertValidAudit(audit);
+      expect(invocation).toThrow(/has no meta.description/);
+    });
+
     it('should throw if failureTitle is missing', () => {
       ExampleAudit.meta.failureTitle = undefined;
       ExampleAudit.meta.scoreDisplayMode = BaseAudit.SCORING_MODES.BINARY;