diff --git a/packages/core/integration-tests/test/html.js b/packages/core/integration-tests/test/html.js
index 5ec98f3b388..d8d022a1dbf 100644
--- a/packages/core/integration-tests/test/html.js
+++ b/packages/core/integration-tests/test/html.js
@@ -329,8 +329,8 @@ describe('html', function() {
 
     // mergeStyles
     assert(
-      html.includes(
-        '<style>h1{color:red}div{font-size:20px}</style><style media="print">div{color:#00f}</style>',
+      html.match(
+        /<style>h1{color:red}div{font-size:20px}\n\/\*# sourceMappingURL=.*\*\/<\/style><style media="print">div{color:#00f}\n\/\*# sourceMappingURL=.*\*\/<\/style>/,
       ),
     );
 
@@ -834,7 +834,11 @@ describe('html', function() {
       path.join(distDir, 'index.html'),
       'utf8',
     );
-    assert(html.includes('<style>.index{color:#00f}</style>'));
+    assert(
+      html.match(
+        /<style>.index{color:#00f}\n\/\*# sourceMappingURL=.*<\/style>/,
+      ),
+    );
   });
 
   it('should process inline non-js scripts', async function() {
@@ -1159,8 +1163,8 @@ describe('html', function() {
       path.join(distDir, html.match(/\/a\.[a-z0-9]+\.css/)[0]),
       'utf8',
     );
-    assert(css.includes('.a'));
-    assert(!css.includes('.b'));
+    assert(css.includes('.a {'));
+    assert(!css.includes('.b {'));
 
     // b.html should point to a CSS bundle containing only b.css
     // It should not point to the bundle containing a.css from a.html
diff --git a/packages/core/integration-tests/test/javascript.js b/packages/core/integration-tests/test/javascript.js
index fb89e0e8459..7ca0be63c9f 100644
--- a/packages/core/integration-tests/test/javascript.js
+++ b/packages/core/integration-tests/test/javascript.js
@@ -2099,15 +2099,17 @@ describe('javascript', function() {
       path.join(__dirname, '/integration/bundle-text/index.js'),
     );
 
-    assert.equal(
-      (await run(b)).default,
-      `body {
+    assert(
+      (await run(b)).default.startsWith(
+        `body {
   background-color: #000000;
 }
 
 .svg-img {
   background-image: url("data:image/svg+xml,%3Csvg%3E%0A%0A%3C%2Fsvg%3E%0A");
-}`,
+}
+/*# sourceMappingURL=data:application/json;charset=utf-8;base64,`,
+      ),
     );
   });
 
diff --git a/packages/core/integration-tests/test/less.js b/packages/core/integration-tests/test/less.js
index 889a53dc281..27d97e06555 100644
--- a/packages/core/integration-tests/test/less.js
+++ b/packages/core/integration-tests/test/less.js
@@ -108,7 +108,7 @@ describe('less', function() {
     assert.equal(output(), 2);
 
     let css = await outputFS.readFile(path.join(distDir, 'index.css'), 'utf8');
-    assert.equal(css, '');
+    assert.equal(css.trim(), '/*# sourceMappingURL=index.css.map */');
   });
 
   it('should support linking to assets with url() from less', async function() {
diff --git a/packages/core/integration-tests/test/sass.js b/packages/core/integration-tests/test/sass.js
index 8671106e540..1d3e4801ad5 100644
--- a/packages/core/integration-tests/test/sass.js
+++ b/packages/core/integration-tests/test/sass.js
@@ -101,7 +101,7 @@ describe('sass', function() {
     assert.equal(output(), 2);
 
     let css = await outputFS.readFile(path.join(distDir, 'index.css'), 'utf8');
-    assert.equal(css, '');
+    assert.equal(css.trim(), '/*# sourceMappingURL=index.css.map */');
   });
 
   it('should support linking to assets with url() from scss', async function() {
diff --git a/packages/core/test-utils/src/utils.js b/packages/core/test-utils/src/utils.js
index f492b4ea454..06138cdb14c 100644
--- a/packages/core/test-utils/src/utils.js
+++ b/packages/core/test-utils/src/utils.js
@@ -508,7 +508,10 @@ function prepareNodeContext(filePath, globals) {
   return ctx;
 }
 
-export function shallowEqual(a, b) {
+export function shallowEqual(
+  a: $Shape<{|+[string]: mixed|}>,
+  b: $Shape<{|+[string]: mixed|}>,
+) {
   if (Object.keys(a).length !== Object.keys(b).length) {
     return false;
   }