Extend test for log-parser

I have seen several "Community Solutions" for this exercise which were
not correct:

  def valid_line?(line) do
    line =~ ~r/^\[DEBUG|INFO|WARNING|ERROR\]/
  end

This would yield wrong result for some lines, which are now covered by
the test.

exercises/concept/log-parser/test/log_parser_test.exs

@@ -33,8 +33,31 @@ defmodule LogParserTest do
     end
 
     @tag task_id: 1
-    test "level must be wrapped in square brackets" do
+    test "DEBUG level must be wrapped in square brackets" do
+      assert LogParser.valid_line?("DEBUG something really bad happened") == false
+      assert LogParser.valid_line?("[DEBUG something really bad happened") == false
+      assert LogParser.valid_line?("DEBUG] something really bad happened") == false
+    end
+
+    @tag task_id: 1
+    test "INFO level must be wrapped in square brackets" do
+      assert LogParser.valid_line?("INFO something really bad happened") == false
+      assert LogParser.valid_line?("[INFO something really bad happened") == false
+      assert LogParser.valid_line?("INFO] something really bad happened") == false
+    end
+
+    @tag task_id: 1
+    test "WARNING level must be wrapped in square brackets" do
+      assert LogParser.valid_line?("WARNING something really bad happened") == false
+      assert LogParser.valid_line?("[WARNING something really bad happened") == false
+      assert LogParser.valid_line?("WARNING] something really bad happened") == false
+    end
+
+    @tag task_id: 1
+    test "ERROR level must be wrapped in square brackets" do
       assert LogParser.valid_line?("ERROR something really bad happened") == false
+      assert LogParser.valid_line?("[ERROR something really bad happened") == false
+      assert LogParser.valid_line?("ERROR] something really bad happened") == false
     end
 
     @tag task_id: 1