diff --git a/packages/opentelemetry-core/test/baggage/W3CBaggagePropagator.test.ts b/packages/opentelemetry-core/test/baggage/W3CBaggagePropagator.test.ts
index 801496513fa..50f110d74a7 100644
--- a/packages/opentelemetry-core/test/baggage/W3CBaggagePropagator.test.ts
+++ b/packages/opentelemetry-core/test/baggage/W3CBaggagePropagator.test.ts
@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 import {
   Baggage,
   BaggageEntry,
@@ -22,10 +21,10 @@ import {
   propagation,
   baggageEntryMetadataFromString,
 } from '@opentelemetry/api';
+import { W3CBaggagePropagator } from '../../src/baggage/propagation/W3CBaggagePropagator.js';
+import { BAGGAGE_HEADER } from '../../src/baggage/constants.js';
 import { ROOT_CONTEXT } from '@opentelemetry/api';
 import * as assert from 'assert';
-import { W3CBaggagePropagator } from '../../src/baggage/propagation/W3CBaggagePropagator';
-import { BAGGAGE_HEADER } from '../../src/baggage/constants';
 
 describe('W3CBaggagePropagator', () => {
   const httpBaggagePropagator = new W3CBaggagePropagator();
diff --git a/packages/opentelemetry-core/test/common/anchored-clock.test.ts b/packages/opentelemetry-core/test/common/anchored-clock.test.ts
index 4c6aa2d1688..4975ff2a0db 100644
--- a/packages/opentelemetry-core/test/common/anchored-clock.test.ts
+++ b/packages/opentelemetry-core/test/common/anchored-clock.test.ts
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import assert = require('assert');
+import * as assert from 'assert';
 import { AnchoredClock } from '../../src/common/anchored-clock.js';
 import { otperformance } from '../../src/platform/node/performance.js';
 
diff --git a/packages/opentelemetry-core/test/common/attributes.test.ts b/packages/opentelemetry-core/test/common/attributes.test.ts
index 8524135b187..c93901b7553 100644
--- a/packages/opentelemetry-core/test/common/attributes.test.ts
+++ b/packages/opentelemetry-core/test/common/attributes.test.ts
@@ -18,7 +18,7 @@ import * as assert from 'assert';
 import {
   isAttributeValue,
   sanitizeAttributes,
-} from '../../src/common/attributes';
+} from '../../src/common/attributes.js';
 
 describe('attributes', () => {
   describe('#isAttributeValue', () => {
diff --git a/packages/opentelemetry-core/test/common/global-error-handler.test.ts b/packages/opentelemetry-core/test/common/global-error-handler.test.ts
index 9dcdb3036f3..34920c2a536 100644
--- a/packages/opentelemetry-core/test/common/global-error-handler.test.ts
+++ b/packages/opentelemetry-core/test/common/global-error-handler.test.ts
@@ -16,7 +16,10 @@
 
 import * as assert from 'assert';
 import * as sinon from 'sinon';
-import { globalErrorHandler, setGlobalErrorHandler } from '../../src';
+import {
+  globalErrorHandler,
+  setGlobalErrorHandler,
+} from '../../src/common/global-error-handler.js';
 import { Exception } from '@opentelemetry/api';
 
 describe('globalErrorHandler', () => {
diff --git a/packages/opentelemetry-core/test/common/logging-error-handler.test.ts b/packages/opentelemetry-core/test/common/logging-error-handler.test.ts
index e89a69d0396..2026a876640 100644
--- a/packages/opentelemetry-core/test/common/logging-error-handler.test.ts
+++ b/packages/opentelemetry-core/test/common/logging-error-handler.test.ts
@@ -17,7 +17,8 @@
 import { diag } from '@opentelemetry/api';
 import * as assert from 'assert';
 import * as sinon from 'sinon';
-import { ErrorHandler, loggingErrorHandler } from '../../src';
+import { loggingErrorHandler } from '../../src/common/logging-error-handler.js';
+import { ErrorHandler } from '../../src/common/types.js';
 
 describe('loggingErrorHandler', () => {
   let handler: ErrorHandler;
diff --git a/packages/opentelemetry-core/test/common/time.test.ts b/packages/opentelemetry-core/test/common/time.test.ts
index bf691c70717..0a64be3f3d4 100644
--- a/packages/opentelemetry-core/test/common/time.test.ts
+++ b/packages/opentelemetry-core/test/common/time.test.ts
@@ -15,7 +15,7 @@
  */
 
 import * as assert from 'assert';
-import { otperformance as performance } from '../../src/platform';
+import { otperformance as performance } from '../../src/platform/node/performance.js';
 import * as sinon from 'sinon';
 import * as api from '@opentelemetry/api';
 import {
diff --git a/packages/opentelemetry-core/test/internal/exporter.test.ts b/packages/opentelemetry-core/test/internal/exporter.test.ts
index 1ca256d659f..37abc7509e9 100644
--- a/packages/opentelemetry-core/test/internal/exporter.test.ts
+++ b/packages/opentelemetry-core/test/internal/exporter.test.ts
@@ -16,9 +16,9 @@
 
 import * as assert from 'assert';
 import * as sinon from 'sinon';
-import { ExportResult, ExportResultCode } from '../../src';
-import * as suppress from '../../src/trace/suppress-tracing';
-import { _export } from '../../src/internal/exporter';
+import { ExportResult, ExportResultCode } from '../../src/ExportResult.js';
+import * as suppress from '../../src/trace/suppress-tracing.js';
+import { _export } from '../../src/internal/exporter.js';
 
 describe('exporter', () => {
   const sandbox = sinon.createSandbox();
diff --git a/packages/opentelemetry-core/test/internal/validators.test.ts b/packages/opentelemetry-core/test/internal/validators.test.ts
index 58dc7b596d3..235b24ef6da 100644
--- a/packages/opentelemetry-core/test/internal/validators.test.ts
+++ b/packages/opentelemetry-core/test/internal/validators.test.ts
@@ -15,7 +15,7 @@
  */
 
 import * as assert from 'assert';
-import { validateKey, validateValue } from '../../src/internal/validators';
+import { validateKey, validateValue } from '../../src/internal/validators.js';
 
 describe('validators', () => {
   describe('validateKey', () => {
diff --git a/packages/opentelemetry-core/test/platform/RandomIdGenerator.test.ts b/packages/opentelemetry-core/test/platform/RandomIdGenerator.test.ts
index 2400fa6ccca..e9255d98ec0 100644
--- a/packages/opentelemetry-core/test/platform/RandomIdGenerator.test.ts
+++ b/packages/opentelemetry-core/test/platform/RandomIdGenerator.test.ts
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 import * as assert from 'assert';
-import { RandomIdGenerator } from '../../src/platform';
+import { RandomIdGenerator } from '../../src/platform/node/RandomIdGenerator.js';
 
 const idGenerator = new RandomIdGenerator();
 
diff --git a/packages/opentelemetry-core/test/platform/hex-to-base64.test.ts b/packages/opentelemetry-core/test/platform/hex-to-base64.test.ts
index 3249621072f..ec4284b956c 100644
--- a/packages/opentelemetry-core/test/platform/hex-to-base64.test.ts
+++ b/packages/opentelemetry-core/test/platform/hex-to-base64.test.ts
@@ -15,7 +15,7 @@
  */
 
 import * as assert from 'assert';
-import { hexToBase64 } from '../../src/platform';
+import { hexToBase64 } from '../../src/platform/node/hex-to-base64.js';
 
 describe('hexToBase64', () => {
   it('convert hex to base64', () => {
diff --git a/packages/opentelemetry-core/test/trace/AlwaysOffSampler.test.ts b/packages/opentelemetry-core/test/trace/AlwaysOffSampler.test.ts
index bda93eddd38..98cbfecef73 100644
--- a/packages/opentelemetry-core/test/trace/AlwaysOffSampler.test.ts
+++ b/packages/opentelemetry-core/test/trace/AlwaysOffSampler.test.ts
@@ -15,7 +15,7 @@
  */
 import * as assert from 'assert';
 import * as api from '@opentelemetry/api';
-import { AlwaysOffSampler } from '../../src/trace/sampler/AlwaysOffSampler';
+import { AlwaysOffSampler } from '../../src/trace/sampler/AlwaysOffSampler.js';
 
 describe('AlwaysOffSampler', () => {
   it('should reflect sampler name', () => {
diff --git a/packages/opentelemetry-core/test/trace/AlwaysOnSampler.test.ts b/packages/opentelemetry-core/test/trace/AlwaysOnSampler.test.ts
index fce88b19bba..44828bfd048 100644
--- a/packages/opentelemetry-core/test/trace/AlwaysOnSampler.test.ts
+++ b/packages/opentelemetry-core/test/trace/AlwaysOnSampler.test.ts
@@ -15,7 +15,7 @@
  */
 import * as assert from 'assert';
 import * as api from '@opentelemetry/api';
-import { AlwaysOnSampler } from '../../src/trace/sampler/AlwaysOnSampler';
+import { AlwaysOnSampler } from '../../src/trace/sampler/AlwaysOnSampler.js';
 
 describe('AlwaysOnSampler', () => {
   it('should reflect sampler name', () => {
diff --git a/packages/opentelemetry-core/test/trace/ParentBasedSampler.test.ts b/packages/opentelemetry-core/test/trace/ParentBasedSampler.test.ts
index 828a32fa3ea..e350ea38aa9 100644
--- a/packages/opentelemetry-core/test/trace/ParentBasedSampler.test.ts
+++ b/packages/opentelemetry-core/test/trace/ParentBasedSampler.test.ts
@@ -15,11 +15,11 @@
  */
 import * as assert from 'assert';
 import * as api from '@opentelemetry/api';
-import { AlwaysOnSampler } from '../../src/trace/sampler/AlwaysOnSampler';
-import { ParentBasedSampler } from '../../src/trace/sampler/ParentBasedSampler';
+import { AlwaysOnSampler } from '../../src/trace/sampler/AlwaysOnSampler.js';
+import { ParentBasedSampler } from '../../src/trace/sampler/ParentBasedSampler.js';
 import { TraceFlags, SpanKind, trace } from '@opentelemetry/api';
-import { AlwaysOffSampler } from '../../src/trace/sampler/AlwaysOffSampler';
-import { TraceIdRatioBasedSampler } from '../../src';
+import { AlwaysOffSampler } from '../../src/trace/sampler/AlwaysOffSampler.js';
+import { TraceIdRatioBasedSampler } from '../../src/trace/sampler/TraceIdRatioBasedSampler.js';
 
 const traceId = 'd4cda95b652f4a1592b449d5929fda1b';
 const spanId = '6e0c63257de34c92';
diff --git a/packages/opentelemetry-core/test/trace/TraceIdRatioBasedSampler.test.ts b/packages/opentelemetry-core/test/trace/TraceIdRatioBasedSampler.test.ts
index c94534c776f..8e2f6adeb50 100644
--- a/packages/opentelemetry-core/test/trace/TraceIdRatioBasedSampler.test.ts
+++ b/packages/opentelemetry-core/test/trace/TraceIdRatioBasedSampler.test.ts
@@ -16,7 +16,7 @@
 
 import * as assert from 'assert';
 import * as api from '@opentelemetry/api';
-import { TraceIdRatioBasedSampler } from '../../src/trace/sampler/TraceIdRatioBasedSampler';
+import { TraceIdRatioBasedSampler } from '../../src/trace/sampler/TraceIdRatioBasedSampler.js';
 
 const spanContext = (traceId = '1') => ({
   traceId,
diff --git a/packages/opentelemetry-core/test/trace/W3CTraceContextPropagator.test.ts b/packages/opentelemetry-core/test/trace/W3CTraceContextPropagator.test.ts
index 2df3395f50d..14e6ba4afea 100644
--- a/packages/opentelemetry-core/test/trace/W3CTraceContextPropagator.test.ts
+++ b/packages/opentelemetry-core/test/trace/W3CTraceContextPropagator.test.ts
@@ -29,9 +29,9 @@ import {
   W3CTraceContextPropagator,
   TRACE_PARENT_HEADER,
   TRACE_STATE_HEADER,
-} from '../../src/trace/W3CTraceContextPropagator';
-import { suppressTracing } from '../../src/trace/suppress-tracing';
-import { TraceState } from '../../src/trace/TraceState';
+} from '../../src/trace/W3CTraceContextPropagator.js';
+import { suppressTracing } from '../../src/trace/suppress-tracing.js';
+import { TraceState } from '../../src/trace/TraceState.js';
 
 describe('W3CTraceContextPropagator', () => {
   const httpTraceContext = new W3CTraceContextPropagator();
diff --git a/packages/opentelemetry-core/test/trace/tracestate.test.ts b/packages/opentelemetry-core/test/trace/tracestate.test.ts
index 8f4e8501999..9e3500143f7 100644
--- a/packages/opentelemetry-core/test/trace/tracestate.test.ts
+++ b/packages/opentelemetry-core/test/trace/tracestate.test.ts
@@ -15,7 +15,7 @@
  */
 
 import * as assert from 'assert';
-import { TraceState } from '../../src/trace/TraceState';
+import { TraceState } from '../../src/trace/TraceState.js';
 
 describe('TraceState', () => {
   describe('.serialize()', () => {
diff --git a/packages/opentelemetry-core/test/utils/callback.test.ts b/packages/opentelemetry-core/test/utils/callback.test.ts
index 0acf2821e6a..0cdc07be393 100644
--- a/packages/opentelemetry-core/test/utils/callback.test.ts
+++ b/packages/opentelemetry-core/test/utils/callback.test.ts
@@ -16,8 +16,8 @@
 
 import * as assert from 'assert';
 import * as sinon from 'sinon';
-import { BindOnceFuture } from '../../src';
-import { assertRejects } from '../test-utils';
+import { BindOnceFuture } from '../../src/utils/callback.js';
+import { assertRejects } from '../test-utils.js';
 
 describe('callback', () => {
   describe('BindOnceFuture', () => {
diff --git a/packages/opentelemetry-core/test/utils/environment.test.ts b/packages/opentelemetry-core/test/utils/environment.test.ts
index 8fa8b08f1e6..901f7f87fbb 100644
--- a/packages/opentelemetry-core/test/utils/environment.test.ts
+++ b/packages/opentelemetry-core/test/utils/environment.test.ts
@@ -14,16 +14,16 @@
  * limitations under the License.
  */
 
-import { getEnv } from '../../src/platform';
+import { getEnv } from '../../src/platform/node/environment.js';
 import {
   DEFAULT_ENVIRONMENT,
   ENVIRONMENT,
   RAW_ENVIRONMENT,
-} from '../../src/utils/environment';
+} from '../../src/utils/environment.js';
 import * as assert from 'assert';
 import * as sinon from 'sinon';
 import { DiagLogLevel } from '@opentelemetry/api';
-import { TracesSamplerValues } from '../../src';
+import { TracesSamplerValues } from '../../src/utils/sampling.js';
 
 let lastMock: RAW_ENVIRONMENT = {};
 
diff --git a/packages/opentelemetry-core/test/utils/merge.test.ts b/packages/opentelemetry-core/test/utils/merge.test.ts
index 56c08c83215..bbc26dc4dd4 100644
--- a/packages/opentelemetry-core/test/utils/merge.test.ts
+++ b/packages/opentelemetry-core/test/utils/merge.test.ts
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 import * as assert from 'assert';
-import { merge } from '../../src/utils/merge';
+import { merge } from '../../src/utils/merge.js';
 
 const tests: TestResult[] = [];
 
diff --git a/packages/opentelemetry-core/test/utils/promise.test.ts b/packages/opentelemetry-core/test/utils/promise.test.ts
index cf97fdf3b1b..1df5abdb68c 100644
--- a/packages/opentelemetry-core/test/utils/promise.test.ts
+++ b/packages/opentelemetry-core/test/utils/promise.test.ts
@@ -15,8 +15,8 @@
  */
 
 import * as assert from 'assert';
-import { Deferred } from '../../src/utils/promise';
-import { assertRejects } from '../test-utils';
+import { Deferred } from '../../src/utils/promise.js';
+import { assertRejects } from '../test-utils.js';
 
 describe('promise', () => {
   describe('Deferred', () => {
diff --git a/packages/opentelemetry-core/test/utils/url.test.ts b/packages/opentelemetry-core/test/utils/url.test.ts
index 8855cff23c3..f1186e8b0a9 100644
--- a/packages/opentelemetry-core/test/utils/url.test.ts
+++ b/packages/opentelemetry-core/test/utils/url.test.ts
@@ -16,7 +16,7 @@
 
 import * as assert from 'assert';
 
-import { isUrlIgnored } from '../../src';
+import { isUrlIgnored } from '../../src/utils/url.js';
 
 const urlIgnored = 'url should be ignored';
 const urlNotIgnored = 'url should NOT be ignored';
diff --git a/packages/opentelemetry-core/test/utils/wrap.test.ts b/packages/opentelemetry-core/test/utils/wrap.test.ts
index 5c9b91f85de..c57fbc1a0b4 100644
--- a/packages/opentelemetry-core/test/utils/wrap.test.ts
+++ b/packages/opentelemetry-core/test/utils/wrap.test.ts
@@ -16,7 +16,8 @@
 
 import * as assert from 'assert';
 
-import { isWrapped, ShimWrapped } from '../../src';
+import { isWrapped } from '../../src/utils/wrap.js';
+import { ShimWrapped } from '../../src/common/types.js';
 
 function makeWrapped(
   wrapped: unknown,