diff --git a/x-pack/plugin/src/test/resources/rest-api-spec/test/ml/data_frame_analytics_crud.yml b/x-pack/plugin/src/test/resources/rest-api-spec/test/ml/data_frame_analytics_crud.yml
index 903ac36d909..afd6701af14 100644
--- a/x-pack/plugin/src/test/resources/rest-api-spec/test/ml/data_frame_analytics_crud.yml
+++ b/x-pack/plugin/src/test/resources/rest-api-spec/test/ml/data_frame_analytics_crud.yml
@@ -272,7 +272,7 @@ setup:
 "Test put config given dest index contains uppercase chars":
 
   - do:
-      catch: /.*reason=Validation Failed.* Destination index \[Foo\] must be lowercase;.*/
+      catch: /.*Validation Failed.* Destination index \[Foo\] must be lowercase;.*/
       ml.put_data_frame_analytics:
         id: "config-given-dest-index-uppercase"
         body: >
@@ -308,7 +308,7 @@ setup:
 "Test put config with missing concrete source index":
 
   - do:
-      catch: /.*reason=Validation Failed.* no such index \[missing\]/
+      catch: /.*Validation Failed.* no such index \[missing\]/
       ml.put_data_frame_analytics:
         id: "config-with-missing-concrete-source-index"
         body: >
@@ -344,7 +344,7 @@ setup:
 "Test put config with dest index same as source index":
 
   - do:
-      catch: /.*reason=Validation Failed.* Destination index \[index-source\] is included in source expression \[index-source\]/
+      catch: /.*Validation Failed.* Destination index \[index-source\] is included in source expression \[index-source\]/
       ml.put_data_frame_analytics:
         id: "config-with-same-source-dest-index"
         body: >
@@ -380,7 +380,7 @@ setup:
         name: multiple-dest-index
 
   - do:
-      catch: /.*reason=Validation Failed.* no write index is defined for alias \[multiple-dest-index\].*/
+      catch: /.*Validation Failed.* no write index is defined for alias \[multiple-dest-index\].*/
       ml.put_data_frame_analytics:
         id: "config-with-dest-index-matching-multiple-indices"
         body: >
@@ -407,7 +407,7 @@ setup:
         name: dest-alias
 
   - do:
-      catch: /.*reason=Validation Failed.* Destination index \[another-source-index\] is included in source expression \[another-source-index\]/
+      catch: /.*Validation Failed.* Destination index \[another-source-index\] is included in source expression \[another-source-index\]/
       ml.put_data_frame_analytics:
         id: "config-with-dest-index-included-in-source-via-alias"
         body: >
@@ -425,7 +425,7 @@ setup:
 "Test put config with remote source index":
 
   - do:
-      catch: /.*reason=Validation Failed.* remote source indices are not supported/
+      catch: /.*Validation Failed.* remote source indices are not supported/
       ml.put_data_frame_analytics:
         id: "config-with-missing-concrete-source-index"
         body: >
diff --git a/x-pack/plugin/src/test/resources/rest-api-spec/test/ml/start_data_frame_analytics.yml b/x-pack/plugin/src/test/resources/rest-api-spec/test/ml/start_data_frame_analytics.yml
index 8cae555a201..1bac2270662 100644
--- a/x-pack/plugin/src/test/resources/rest-api-spec/test/ml/start_data_frame_analytics.yml
+++ b/x-pack/plugin/src/test/resources/rest-api-spec/test/ml/start_data_frame_analytics.yml
@@ -31,7 +31,7 @@
         index: missing
 
   - do:
-      catch: /.*reason=Validation Failed.* no such index \[missing\]/
+      catch: /.*Validation Failed.* no such index \[missing\]/
       ml.start_data_frame_analytics:
         id: "missing_index"
 
diff --git a/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/preview_transforms.yml b/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/preview_transforms.yml
index cf139b04b44..7abb83834f5 100644
--- a/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/preview_transforms.yml
+++ b/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/preview_transforms.yml
@@ -166,7 +166,7 @@ setup:
 ---
 "Test preview with non-existing source index":
   - do:
-      catch: /.*reason=Validation Failed.* no such index \[does_not_exist\]/
+      catch: /.*Validation Failed.* no such index \[does_not_exist\]/
       transform.preview_transform:
         body: >
           {
diff --git a/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_crud.yml b/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_crud.yml
index b8dc88c3ae0..e66982aadec 100644
--- a/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_crud.yml
+++ b/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_crud.yml
@@ -79,7 +79,7 @@ setup:
 ---
 "Test put transform with invalid source index":
   - do:
-      catch: /.*reason=Validation Failed.* no such index \[missing-index\]/
+      catch: /.*Validation Failed.* no such index \[missing-index\]/
       transform.put_transform:
         transform_id: "missing-source-transform"
         body: >
@@ -400,7 +400,7 @@ setup:
         name: source-index
 
   - do:
-      catch: /.*reason=Validation Failed.* Destination index \[created-destination-index\] is included in source expression \[airline-data,created-destination-index\]/
+      catch: /.*Validation Failed.* Destination index \[created-destination-index\] is included in source expression \[airline-data,created-destination-index\]/
       transform.put_transform:
         transform_id: "transform-from-aliases-failures"
         body: >
@@ -426,7 +426,7 @@ setup:
         name: dest-index
 
   - do:
-      catch: /.*reason=Validation Failed.* no write index is defined for alias [dest2-index].*/
+      catch: /.*Validation Failed.* no write index is defined for alias [dest2-index].*/
       transform.put_transform:
         transform_id: "airline-transform"
         body: >
@@ -537,7 +537,7 @@ setup:
 ---
 "Test invalid destination index name":
   - do:
-      catch: /.*reason=Validation Failed.* Destination index \[DeStInAtIoN\] must be lowercase/
+      catch: /.*Validation Failed.* Destination index \[DeStInAtIoN\] must be lowercase/
       transform.put_transform:
         transform_id: "airline-transform"
         body: >
diff --git a/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_update.yml b/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_update.yml
index f55fcd2cb07..d82bc1bea9d 100644
--- a/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_update.yml
+++ b/x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_update.yml
@@ -67,7 +67,7 @@ setup:
 ---
 "Test put transform with invalid source index":
   - do:
-      catch: /.*reason=Validation Failed.* no such index \[missing-index\]/
+      catch: /.*Validation Failed.* no such index \[missing-index\]/
       transform.update_transform:
         transform_id: "updating-airline-transform"
         body: >
@@ -255,7 +255,7 @@ setup:
         name: source2-index
 
   - do:
-      catch: /.*reason=Validation Failed.* Destination index \[created-destination-index\] is included in source expression \[created-destination-index\]/
+      catch: /.*Validation Failed.* Destination index \[created-destination-index\] is included in source expression \[created-destination-index\]/
       transform.update_transform:
         transform_id: "updating-airline-transform"
         body: >
@@ -280,7 +280,7 @@ setup:
         index: created-destination-index
         name: dest2-index
   - do:
-      catch: /.*reason=Validation Failed.* no write index is defined for alias [dest2-index].*/
+      catch: /.*Validation Failed.* no write index is defined for alias [dest2-index].*/
       transform.update_transform:
         transform_id: "updating-airline-transform"
         body: >
@@ -290,7 +290,7 @@ setup:
 ---
 "Test invalid destination index name":
   - do:
-      catch: /.*reason=Validation Failed.* Destination index \[DeStInAtIoN\] must be lowercase/
+      catch: /.*Validation Failed.* Destination index \[DeStInAtIoN\] must be lowercase/
       transform.update_transform:
         transform_id: "updating-airline-transform"
         body: >
@@ -298,7 +298,7 @@ setup:
             "dest": { "index": "DeStInAtIoN" }
           }
   - do:
-      catch: /.*reason=Validation Failed.* Invalid index name \[destination#dest\], must not contain \'#\'/
+      catch: /.*Validation Failed.* Invalid index name \[destination#dest\], must not contain \'#\'/
       transform.update_transform:
         transform_id: "updating-airline-transform"
         body: >