Add specs for environment filter

spec/filters/environment.rb

@@ -0,0 +1,43 @@
+require "test_utils"
+require "logstash/filters/environment"
+
+describe LogStash::Filters::Environment do
+  extend LogStash::RSpec
+
+  describe "add a field from the environment" do
+    # The logstash config goes here.
+    # At this time, only filters are supported.
+    config <<-CONFIG
+      filter {
+        environment {
+          add_field_from_env => [ "newfield", "MY_ENV_VAR" ]
+        }
+      }
+    CONFIG
+
+    ENV["MY_ENV_VAR"] = "hello world"
+
+    sample "example" do
+      insist { subject["newfield"] } == "hello world"
+    end
+  end
+
+  describe "does nothing on non-matching events" do
+    # The logstash config goes here.
+    # At this time, only filters are supported.
+    config <<-CONFIG
+      filter {
+        environment {
+          type => "foo"
+          add_field_from_env => [ "newfield", "MY_ENV_VAR" ]
+        }
+      }
+    CONFIG
+
+    ENV["MY_ENV_VAR"] = "hello world"
+
+    sample({ "@type" => "bar", "@message" => "fizz", "@fields" => { } }) do
+      insist { subject["newfield"] }.nil?
+    end
+  end
+end