tests: add tests for CSPPlug

test/plugs/csp_plug_test.exs

+defmodule Pleroma.Web.Plugs.CSPPlugTest do
+  use Pleroma.Web.ConnCase
+  alias Pleroma.Config
+  alias Plug.Conn
+
+  test "it sends CSP headers when enabled", %{conn: conn} do
+    Config.put([:csp, :enabled], true)
+
+    conn =
+      conn
+      |> get("/api/v1/instance")
+
+    refute Conn.get_resp_header(conn, "x-xss-protection") == []
+    refute Conn.get_resp_header(conn, "x-permitted-cross-domain-policies") == []
+    refute Conn.get_resp_header(conn, "x-frame-options") == []
+    refute Conn.get_resp_header(conn, "x-content-type-options") == []
+    refute Conn.get_resp_header(conn, "x-download-options") == []
+    refute Conn.get_resp_header(conn, "referrer-policy") == []
+    refute Conn.get_resp_header(conn, "content-security-policy") == []
+  end
+
+  test "it does not send CSP headers when disabled", %{conn: conn} do
+    Config.put([:csp, :enabled], false)
+
+    conn =
+      conn
+      |> get("/api/v1/instance")
+
+    assert Conn.get_resp_header(conn, "x-xss-protection") == []
+    assert Conn.get_resp_header(conn, "x-permitted-cross-domain-policies") == []
+    assert Conn.get_resp_header(conn, "x-frame-options") == []
+    assert Conn.get_resp_header(conn, "x-content-type-options") == []
+    assert Conn.get_resp_header(conn, "x-download-options") == []
+    assert Conn.get_resp_header(conn, "referrer-policy") == []
+    assert Conn.get_resp_header(conn, "content-security-policy") == []
+  end
+
+  test "it sends STS headers when enabled", %{conn: conn} do
+    Config.put([:csp, :enabled], true)
+    Config.put([:csp, :sts], true)
+
+    conn =
+      conn
+      |> get("/api/v1/instance")
+
+    refute Conn.get_resp_header(conn, "strict-transport-security") == []
+    refute Conn.get_resp_header(conn, "expect-ct") == []
+  end
+
+  test "it does not send STS headers when disabled", %{conn: conn} do
+    Config.put([:csp, :enabled], true)
+    Config.put([:csp, :sts], false)
+
+    conn =
+      conn
+      |> get("/api/v1/instance")
+
+    assert Conn.get_resp_header(conn, "strict-transport-security") == []
+    assert Conn.get_resp_header(conn, "expect-ct") == []
+  end
+end