diff --git a/packages/eslint-plugin/tests/rules/non-nullable-type-assertion-style.test.ts b/packages/eslint-plugin/tests/rules/non-nullable-type-assertion-style.test.ts
index 4b0750c8c84..365de88c36a 100644
--- a/packages/eslint-plugin/tests/rules/non-nullable-type-assertion-style.test.ts
+++ b/packages/eslint-plugin/tests/rules/non-nullable-type-assertion-style.test.ts
@@ -1,14 +1,11 @@
-import path from 'path';
-
 import rule from '../../src/rules/non-nullable-type-assertion-style';
-import { RuleTester } from '../RuleTester';
+import { getFixturesRootDir, RuleTester } from '../RuleTester';
 
-const rootDir = path.resolve(__dirname, '../fixtures/');
 const ruleTester = new RuleTester({
   parserOptions: {
     sourceType: 'module',
-    tsconfigRootDir: rootDir,
-    project: './tsconfig.noUncheckedIndexedAccess.json',
+    tsconfigRootDir: getFixturesRootDir(),
+    project: './tsconfig.json',
   },
   parser: '@typescript-eslint/parser',
 });
@@ -62,35 +59,6 @@ const x = 1 as 1;
 declare function foo<T = any>(): T;
 const bar = foo() as number;
     `,
-    `
-function first<T>(array: ArrayLike<T>): T | null {
-  return array.length > 0 ? (array[0] as T) : null;
-}
-    `,
-    `
-function first<T extends string | null>(array: ArrayLike<T>): T | null {
-  return array.length > 0 ? (array[0] as T) : null;
-}
-    `,
-    `
-function first<T extends string | undefined>(array: ArrayLike<T>): T | null {
-  return array.length > 0 ? (array[0] as T) : null;
-}
-    `,
-    `
-function first<T extends string | null | undefined>(
-  array: ArrayLike<T>,
-): T | null {
-  return array.length > 0 ? (array[0] as T) : null;
-}
-    `,
-    `
-type A = 'a' | 'A';
-type B = 'b' | 'B';
-function first<T extends A | B | null>(array: ArrayLike<T>): T | null {
-  return array.length > 0 ? (array[0] as T) : null;
-}
-    `,
   ],
 
   invalid: [
@@ -229,24 +197,73 @@ declare const x: T;
 const y = x!;
       `,
     },
-    {
-      code: `
-function first<T extends string | number>(array: ArrayLike<T>): T | null {
+  ],
+});
+
+const ruleTesterWithNoUncheckedIndexAccess = new RuleTester({
+  parserOptions: {
+    sourceType: 'module',
+    tsconfigRootDir: getFixturesRootDir(),
+    project: './tsconfig.noUncheckedIndexedAccess.json',
+  },
+  parser: '@typescript-eslint/parser',
+});
+
+ruleTesterWithNoUncheckedIndexAccess.run(
+  'non-nullable-type-assertion-style - noUncheckedIndexedAccess',
+  rule,
+  {
+    valid: [
+      `
+function first<T>(array: ArrayLike<T>): T | null {
   return array.length > 0 ? (array[0] as T) : null;
 }
       `,
-      errors: [
-        {
-          column: 30,
-          line: 3,
-          messageId: 'preferNonNullAssertion',
-        },
-      ],
-      output: `
+      `
+function first<T extends string | null>(array: ArrayLike<T>): T | null {
+  return array.length > 0 ? (array[0] as T) : null;
+}
+      `,
+      `
+function first<T extends string | undefined>(array: ArrayLike<T>): T | null {
+  return array.length > 0 ? (array[0] as T) : null;
+}
+      `,
+      `
+function first<T extends string | null | undefined>(
+  array: ArrayLike<T>,
+): T | null {
+  return array.length > 0 ? (array[0] as T) : null;
+}
+      `,
+      `
+type A = 'a' | 'A';
+type B = 'b' | 'B';
+function first<T extends A | B | null>(array: ArrayLike<T>): T | null {
+  return array.length > 0 ? (array[0] as T) : null;
+}
+      `,
+    ],
+    invalid: [
+      {
+        code: `
+function first<T extends string | number>(array: ArrayLike<T>): T | null {
+  return array.length > 0 ? (array[0] as T) : null;
+}
+        `,
+        errors: [
+          {
+            column: 30,
+            line: 3,
+            messageId: 'preferNonNullAssertion',
+          },
+        ],
+        output: `
 function first<T extends string | number>(array: ArrayLike<T>): T | null {
   return array.length > 0 ? (array[0]!) : null;
 }
-      `,
-    },
-  ],
-});
+        `,
+      },
+    ],
+  },
+);
diff --git a/packages/typescript-estree/src/create-program/createWatchProgram.ts b/packages/typescript-estree/src/create-program/createWatchProgram.ts
index 0e32f8ec1e5..d17835fff3c 100644
--- a/packages/typescript-estree/src/create-program/createWatchProgram.ts
+++ b/packages/typescript-estree/src/create-program/createWatchProgram.ts
@@ -159,11 +159,21 @@ function getProgramsForProjects(parseSettings: ParseSettings): ts.Program[] {
     );
   }
 
+  const currentProjectsFromSettings = new Set(parseSettings.projects);
+
   /*
    * before we go into the process of attempting to find and update every program
    * see if we know of a program that contains this file
    */
   for (const [tsconfigPath, existingWatch] of knownWatchProgramMap.entries()) {
+    if (!currentProjectsFromSettings.has(tsconfigPath)) {
+      // the current parser run doesn't specify this tsconfig in parserOptions.project
+      // so we don't want to consider it for caching purposes.
+      //
+      // if we did consider it we might return a program for a project
+      // that wasn't specified in the current parser run (which is obv bad!).
+      continue;
+    }
     let fileList = programFileListCache.get(tsconfigPath);
     let updatedProgram: ts.Program | null = null;
     if (!fileList) {