diff --git a/package.json b/package.json
index 2f4d331..b0147bd 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,7 @@
   "scripts": {
     "prepublishOnly": "npm run build",
     "build": "microbundle -i src/index.ts -f es,cjs",
-    "test": "typed-test --typeCheck 'src/**/*.test.ts'"
+    "test": "typed-test --typeCheck 'src/**/*.__test__.ts'"
   },
   "keywords": [
     "most",
diff --git a/src/index.__test__.ts b/src/index.__test__.ts
new file mode 100644
index 0000000..cfe2cb4
--- /dev/null
+++ b/src/index.__test__.ts
@@ -0,0 +1,164 @@
+import {
+  count,
+  index,
+  indexed,
+  keepIndex,
+  withCount,
+  withIndex,
+  withIndexStart
+} from "./index";
+import { constant, periodic, runEffects, take, tap } from "@most/core";
+import { newDefaultScheduler } from "@most/scheduler";
+import { Stream } from "@most/types";
+import { describe, it, given } from "@typed/test";
+
+const TEST_EVENT_VALUE = "test";
+
+const collect = async <A>(n: number, s: Stream<A>): Promise<A[]> => {
+  const xs: A[] = [];
+  const sa = tap(x => xs.push(x), s);
+  await runEffects(take(n, sa), newDefaultScheduler());
+  return xs;
+};
+
+const range = (start: number, n: number): number[] =>
+  Array.from(Array(n), (_, i) => start + i);
+
+const randomInt = (min: number, max: number) =>
+  min + Math.floor(Math.random() * (max - min));
+
+export const indexTests = describe("index", [
+  given("a stream", [
+    it("replaces events with 0-based index", async ({ equal }) => {
+      // Fixture setup
+      const s = periodic(1);
+      const n = randomInt(10, 20);
+      const expectedEvents = range(0, n);
+      // Exercise system
+      const result = index(s);
+      // Verify outcome
+      const actualEvents = await collect(n, result);
+      equal(expectedEvents, actualEvents);
+    })
+  ])
+]);
+
+export const withIndexTests = describe("withIndex", [
+  given("a stream", [
+    it("pairs events with 0-based count", async ({ equal }) => {
+      // Fixture setup
+      const s = constant(TEST_EVENT_VALUE, periodic(1));
+      const n = randomInt(10, 20);
+      const expectedEvents = range(0, n).map<[number, string]>(n => [
+        n,
+        TEST_EVENT_VALUE
+      ]);
+      // Exercise system
+      const result = withIndex(s);
+      // Verify outcome
+      const actualEvents = await collect(n, result);
+      equal(expectedEvents, actualEvents);
+    })
+  ])
+]);
+
+export const countTests = describe("count", [
+  given("a stream", [
+    it("replaces events with 1-based count", async ({ equal }) => {
+      // Fixture setup
+      const s = periodic(1);
+      const n = randomInt(10, 20);
+      const expectedEvents = range(1, n);
+      // Exercise system
+      const result = count(s);
+      // Verify outcome
+      const actualEvents = await collect(n, result);
+      equal(expectedEvents, actualEvents);
+    })
+  ])
+]);
+
+export const withCountTests = describe("withCount", [
+  given("a stream", [
+    it("pairs events with 1-based count", async ({ equal }) => {
+      // Fixture setup
+      const s = constant(TEST_EVENT_VALUE, periodic(1));
+      const n = randomInt(10, 20);
+      const expectedEvents = range(1, n).map<[number, string]>(n => [
+        n,
+        TEST_EVENT_VALUE
+      ]);
+      // Exercise system
+      const result = withCount(s);
+      // Verify outcome
+      const actualEvents = await collect(n, result);
+      equal(expectedEvents, actualEvents);
+    })
+  ])
+]);
+
+export const withIndexStartTests = describe("withIndexStart", [
+  given("a start index and a stream", [
+    it("pairs events with start-based index", async ({ equal }) => {
+      // Fixture setup
+      const idx = randomInt(0, 10000);
+      const s = constant(TEST_EVENT_VALUE, periodic(1));
+      const n = randomInt(10, 20);
+      const expectedEvents = range(idx, n).map<[number, string]>(n => [
+        n,
+        TEST_EVENT_VALUE
+      ]);
+      // Exercise system
+      const result = withIndexStart(idx, s);
+      // Verify outcome
+      const actualEvents = await collect(n, result);
+      equal(expectedEvents, actualEvents);
+    })
+  ])
+]);
+
+export const indexedTests = describe("indexed", [
+  given("a function, an initial value, and a stream", [
+    it("should pair events with computed index", async ({ equal }) => {
+      // Fixture setup
+      const n = randomInt(10, 20);
+      const arbitraryChar = "a";
+      const strOfLenN = Array(n)
+        .fill(arbitraryChar)
+        .join("");
+      const stringIndex = (s: string) => (prev: string): [string, string] => [
+        prev,
+        prev + s
+      ];
+      const f = stringIndex(arbitraryChar);
+      const init = "";
+      const s = constant(TEST_EVENT_VALUE, periodic(1));
+      const expectedEvents = range(0, n).map<[string, string]>((_, i) => [
+        strOfLenN.slice(0, i),
+        TEST_EVENT_VALUE
+      ]);
+      // Exercise system
+      const result = indexed(f, init, s);
+      // Verify outcome
+      const actualEvents = await collect(n, result);
+      equal(expectedEvents, actualEvents);
+    })
+  ])
+]);
+
+export const keepIndexTests = describe("keepIndex", [
+  given("a stream of an [index, value] pair", [
+    it("should keep index and discard value", async ({ equal }) => {
+      // Fixture setup
+      const idx = randomInt(0, 10000);
+      const s = withIndexStart(idx, constant(TEST_EVENT_VALUE, periodic(1)));
+      const n = randomInt(10, 20);
+      const expectedEvents = range(idx, n);
+      // Exercise system
+      const result = keepIndex(s);
+      // Verify outcome
+      const actualEvents = await collect(n, result);
+      equal(expectedEvents, actualEvents);
+    })
+  ])
+]);
diff --git a/src/index.test.ts b/src/index.test.ts
deleted file mode 100644
index 2de9099..0000000
--- a/src/index.test.ts
+++ /dev/null
@@ -1,83 +0,0 @@
-import { count, index, indexed, keepIndex, withCount, withIndex, withIndexStart } from './index'
-import { constant, periodic, runEffects, take, tap } from '@most/core'
-import { newDefaultScheduler } from '@most/scheduler'
-import { Stream } from '@most/types'
-import { describe, it } from '@typed/test'
-
-const collect = async<A>(n: number, s: Stream<A>): Promise<A[]> => {
-  const eventValues: A[] = []
-  const collectStream = tap(x => eventValues.push(x), s)
-  await runEffects(take(n, collectStream), newDefaultScheduler())
-  return eventValues
-}
-
-const range = (start: number, n: number): number[] =>
-  Array.from(Array(n), (_, i) => start + i)
-
-const randomInt = (min: number, max: number) =>
-  min + Math.floor(Math.random() * (max - min))
-
-export const indexTests = describe('index', [
-  it('replaces events with 0-based index', async ({ equal }) => {
-    const n = randomInt(10, 20)
-    const events = await collect(n, index(periodic(1)))
-    equal(range(0, n), events)
-  })
-])
-
-export const withIndexTests = describe('withIndex', [
-  it('pairs events with 0-based count', async ({ equal }) => {
-    const n = randomInt(10, 20)
-    const events = await collect(n, withIndex(constant('test', periodic(1))))
-    equal(range(0, n).map(x => [x, 'test']), events)
-  })
-])
-
-export const countTests = describe('count', [
-  it('replaces events with 1-based count', async ({ equal }) => {
-    const n = randomInt(10, 20)
-    const events = await collect(n, count(periodic(1)))
-    equal(range(1, n), events)
-  })
-])
-
-export const withCountTests = describe('withCount', [
-  it('pairs events with 1-based count', async ({ equal }) => {
-    const n = randomInt(10, 20)
-    const events = await collect(n, withCount(constant('test', periodic(1))))
-    equal(range(1, n).map(x => [x, 'test']), events)
-  })
-])
-
-export const withIndexStartTests = describe('withIndexStart', [
-  it('pairs events with start-based index', async ({ equal }) => {
-    const start = randomInt(0, 10000)
-    const n = randomInt(10, 20)
-    const events = await collect(n, withIndexStart(start, constant('test', periodic(1))))
-    equal(range(start, n).map(x => [x, 'test']), events)
-  })
-])
-
-export const indexedTests = describe('indexed', [
-  it('pairs events with computed index', async ({ equal }) => {
-    const n = randomInt(10, 20)
-
-    const s = Array(n).fill('a').join('')
-    const expected = range(0, n).map((_, i) => [s.slice(0, i), 'test'])
-
-    const stringIndex = (s: string) => (prev: string): [string, string] =>
-      [prev, prev + s]
-
-    const events = await collect(n, indexed(stringIndex('a'), '', constant('test', periodic(1))))
-    equal(expected, events)
-  })
-])
-
-export const keepIndexTests = describe('keepIndex', [
-  it('keeps index and discards value', async ({ equal }) => {
-    const start = randomInt(0, 10000)
-    const n = randomInt(10, 20)
-    const events = await collect(n, keepIndex(withIndexStart(start, constant('test', periodic(1)))))
-    equal(range(start, n), events)
-  })
-])
\ No newline at end of file
diff --git a/tsconfig.base.json b/tsconfig.base.json
new file mode 100644
index 0000000..e80a90b
--- /dev/null
+++ b/tsconfig.base.json
@@ -0,0 +1,21 @@
+{
+  "compilerOptions": {
+    "target": "es5",
+    "module": "es2015",
+    "moduleResolution": "node",
+    "lib": ["es2015", "es2016", "es2017"],
+    "declaration": true,
+    "sourceMap": true,
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noImplicitAny": true,
+    "noImplicitReturns": true,
+    "noFallthroughCasesInSwitch": true,
+    "strictNullChecks": true,
+    "strictFunctionTypes": true,
+    "allowSyntheticDefaultImports": true,
+    "esModuleInterop": true
+  },
+  "exclude": ["node_modules", "src/**/*.__test__.ts"]
+}
diff --git a/tsconfig.json b/tsconfig.json
index 7b8b447..8eeb7d6 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,31 +1,7 @@
 {
+  "extends": "./tsconfig.base.json",
   "compilerOptions": {
-    "moduleResolution": "node",
-    "target": "es5",
-    "module": "es2015",
-    "lib": [
-      "es5",
-      "es2015",
-      "es2016",
-      "es2017"
-    ],
-    "incremental": true,
-    "strict": true,
-    "sourceMap": true,
-    "declaration": true,
-    "declarationDir": "dist",
-    "outDir": "dist",
-    "typeRoots": [
-      "node_modules/@types"
-    ]
+    "outDir": "dist"
   },
-  "exclude": [
-    "experiments/**/*.ts",
-    "examples/**/*.ts",
-    "node_modules",
-    "src/**/*.test.ts"
-  ],
-  "include": [
-    "src"
-  ]
+  "include": ["src/**/*.ts"]
 }
diff --git a/tsconfig.test.json b/tsconfig.test.json
new file mode 100644
index 0000000..b9c47be
--- /dev/null
+++ b/tsconfig.test.json
@@ -0,0 +1,9 @@
+{
+  "extends": "./tsconfig.base.json",
+  "compilerOptions": {
+    "lib": ["dom", "es2015", "es2016", "es2017"],
+    "outDir": "__test__"
+  },
+  "include": ["src/**/*.__test__.ts"],
+  "exclude": ["node_modules"]
+}