rake db:structure:dump warns when `mysqldump` is not in PATH.

Closes #9518.

The rake task used to fail silently and left an empty `structure.sql`.
It's confusing for users to get to the root of the problem.
The warning message tells them where to look.

1 files changed, 12 insertions, 1 deletions

diff --git a/activerecord/test/cases/tasks/mysql_rake_test.rb b/activerecord/test/cases/tasks/mysql_rake_test.rb
index 38b9dd02f0..dadcca5b7f 100644
--- a/activerecord/test/cases/tasks/mysql_rake_test.rb
+++ b/activerecord/test/cases/tasks/mysql_rake_test.rb
@@ -249,10 +249,21 @@ module ActiveRecord
 
     def test_structure_dump
       filename = "awesome-file.sql"
-      Kernel.expects(:system).with("mysqldump", "--result-file", filename, "--no-data", "test-db")
+      Kernel.expects(:system).with("mysqldump", "--result-file", filename, "--no-data", "test-db").returns(true)
 
       ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
     end
+
+    def test_warn_when_external_structure_dump_fails
+      filename = "awesome-file.sql"
+      Kernel.expects(:system).with("mysqldump", "--result-file", filename, "--no-data", "test-db").returns(false)
+
+      warnings = capture(:stderr) do
+        ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
+      end
+
+      assert_match(/Could not dump the database structure/, warnings)
+    end
   end
 
   class MySQLStructureLoadTest < ActiveRecord::TestCase