Issue #2123225 by Jelle_S, attiks, Risse, bradklaver | Wim Leers: Fixed Do not upscale by default.

core/modules/image/config/install/image.style.large.yml

@@ -6,7 +6,7 @@ effects:
     data:
       width: 480
       height: 480
-      upscale: true
+      upscale: false
     weight: 0
     uuid: ddd73aa7-4bd6-4c85-b600-bdf2b1628d1d
 langcode: en

core/modules/image/config/install/image.style.medium.yml

@@ -6,7 +6,7 @@ effects:
     data:
       width: 220
       height: 220
-      upscale: true
+      upscale: false
     weight: 0
     uuid: bddf0d06-42f9-4c75-a700-a33cafa25ea0
 langcode: en

core/modules/image/config/install/image.style.thumbnail.yml

@@ -6,7 +6,7 @@ effects:
     data:
       width: 100
       height: 100
-      upscale: true
+      upscale: false
     weight: 0
     uuid: 1cfec298-8620-4749-b100-ccb6c4500779
 langcode: en

core/modules/image/src/Tests/ImageFieldDisplayTest.php

@@ -143,8 +143,8 @@ class ImageFieldDisplayTest extends ImageFieldTestBase {
     $image_style = array(
       '#theme' => 'image_style',
       '#uri' => $image_uri,
-      '#width' => 100,
-      '#height' => 50,
+      '#width' => 40,
+      '#height' => 20,
       '#style_name' => 'thumbnail',
     );
     $default_output = drupal_render($image_style);
@@ -199,8 +199,8 @@ class ImageFieldDisplayTest extends ImageFieldTestBase {
     $image_style = array(
       '#theme' => 'image_style',
       '#uri' => file_load($node->{$field_name}->target_id)->getFileUri(),
-      '#width' => 220,
-      '#height' => 110,
+      '#width' => 40,
+      '#height' => 20,
       '#style_name' => 'medium',
     );
     $default_output = drupal_render($image_style);

core/modules/responsive_image/src/Tests/ResponsiveImageFieldDisplayTest.php

@@ -165,7 +165,7 @@ class ResponsiveImageFieldDisplayTest extends ImageFieldTestBase {
     $fallback_image = array(
       '#theme' => 'responsive_image_source',
       '#src' => $large_style->buildUrl($image_uri),
-      '#dimensions' => array('width' => 480, 'height' => 240),
+      '#dimensions' => array('width' => 40, 'height' => 20),
     );
     $default_output = drupal_render($fallback_image);
     $this->assertRaw($default_output, 'Image style thumbnail formatter displaying correctly on full node view.');