test: add middleware and static file tests

test/test_middleware_params.rb

@@ -0,0 +1,43 @@
+require 'minitest/autorun'
+require 'prism'
+require 'support'
+
+class MiddlewareParamsTest < Minitest::Test
+  include TestSupport
+
+  def setup
+    @seen_env = nil
+    downstream = lambda do |env|
+      @seen_env = env
+      [200, {}, ['ok']]
+    end
+    @app = Prism::Middleware::ParamsParser.new(downstream)
+  end
+
+  def test_valid_json_body_passes_through
+    env = env_for('POST', '/echo', headers: { 'Content-Type' => 'application/json' }, body: '{"a":1}')
+    status, = @app.call(env)
+    assert_equal 200, status
+  end
+
+  def test_malformed_json_body_returns_400_before_reaching_app
+    env = env_for('POST', '/echo', headers: { 'Content-Type' => 'application/json' }, body: '{not-json')
+    status, headers, body = @app.call(env)
+    assert_equal 400, status
+    assert_equal 'application/json', headers['Content-Type']
+    assert_includes JSON.parse(body.join)['error'], 'invalid JSON'
+    assert_nil @seen_env, 'downstream app must not run on malformed body'
+  end
+
+  def test_downstream_can_still_read_the_body_after_validation
+    env = env_for('POST', '/echo', headers: { 'Content-Type' => 'application/json' }, body: '{"a":1}')
+    @app.call(env)
+    assert_equal({ 'a' => 1 }, JSON.parse(@seen_env['rack.input'].read))
+  end
+
+  def test_non_json_body_is_left_alone
+    env = env_for('POST', '/echo', headers: { 'Content-Type' => 'application/x-www-form-urlencoded' }, body: 'a=1')
+    status, = @app.call(env)
+    assert_equal 200, status
+  end
+end