test(core): add unit tests for untested core modules

Adds 113 tests covering:
- abc: RegistryABC (concrete implementation + edge cases)
- environment: Environment get/set, EnvironmentEnum
- pipes: BoolPipe, IPAddressPipe (incl. roundtrip + error cases)
- time: Cron (next(), intervals, invalid expression)
- utils: Cache (TTL, expiry, cleanup), get_value (incl. bug
  documentation: cast result not returned for string->typed values),
  JSONProcessor (nested objects, enums, defaults)
- property: classproperty (class access, instance access, subclass)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/core/environment/environment_test.py

@@ -0,0 +1,92 @@
+import os
+import pytest
+from cpl.core.environment.environment import Environment
+from cpl.core.environment.environment_enum import EnvironmentEnum
+
+
+def test_set_and_get_environment_valid():
+    for env in EnvironmentEnum:
+        Environment.set_environment(env.value)
+        assert Environment.get_environment() == env.value
+
+
+def test_set_environment_invalid():
+    with pytest.raises(AssertionError):
+        Environment.set_environment("invalid_env")
+
+
+def test_set_environment_empty():
+    with pytest.raises(AssertionError):
+        Environment.set_environment("")
+
+
+def test_set_environment_none():
+    with pytest.raises(AssertionError):
+        Environment.set_environment(None)
+
+
+def test_set_and_get_app_name():
+    Environment.set_app_name("TestApp")
+    assert Environment.get_app_name() == "TestApp"
+
+
+def test_get_host_name():
+    hostname = Environment.get_host_name()
+    assert isinstance(hostname, str)
+    assert len(hostname) > 0
+
+
+def test_get_cwd():
+    cwd = Environment.get_cwd()
+    assert isinstance(cwd, str)
+    assert os.path.isdir(cwd)
+
+
+def test_set_cwd(tmp_path):
+    original = Environment.get_cwd()
+    Environment.set_cwd(str(tmp_path))
+    assert Environment.get_cwd() == str(tmp_path)
+    Environment.set_cwd(original)
+
+
+def test_set_cwd_empty():
+    with pytest.raises(AssertionError):
+        Environment.set_cwd("")
+
+
+def test_set_cwd_none():
+    with pytest.raises(AssertionError):
+        Environment.set_cwd(None)
+
+
+def test_set_and_get_generic():
+    Environment.set("CPL_TEST_KEY", "hello")
+    assert Environment.get("CPL_TEST_KEY", str) == "hello"
+
+
+def test_get_missing_key_returns_default():
+    result = Environment.get("CPL_NONEXISTENT_KEY_XYZ", str, "default_value")
+    assert result == "default_value"
+
+
+def test_get_missing_key_returns_none():
+    result = Environment.get("CPL_NONEXISTENT_KEY_XYZ2", str)
+    assert result is None
+
+
+def test_set_key_empty():
+    with pytest.raises(AssertionError):
+        Environment.set("", "value")
+
+
+def test_set_key_none():
+    with pytest.raises(AssertionError):
+        Environment.set(None, "value")
+
+
+def test_environment_enum_values():
+    values = [e.value for e in EnvironmentEnum]
+    assert "production" in values
+    assert "staging" in values
+    assert "testing" in values
+    assert "development" in values