Add a test & readme clarification about schemas in lazy loading

README.rst

@@ -182,6 +182,9 @@ like ``apispec`` and requires an application instance available, then you can pa
 
 In this case the test body will be used as a sub-test via ``pytest-subtests`` library.
 
+**NOTE**: the used fixture should return a valid schema that could be created via ``schemathesis.from_dict`` or other
+``schemathesis.from_`` variations.
+
 Documentation
 -------------
 

test/test_lazy.py

@@ -47,3 +47,31 @@ def test_(request, case, another):
     result.assert_outcomes(passed=1)
     result.stdout.re_match_lines([r"test_with_fixtures.py::test_ PASSED", r".*1 passed"])
     result.stdout.re_match_lines([r"Hypothesis calls: 1"])
+
+
+def test_invalid_fixture(testdir):
+    # When the test uses a schema fixture that doesn't return a BaseSchema subtype
+    testdir.make_test(
+        """
+@pytest.fixture
+def simple_schema():
+    return 1
+
+lazy_schema = schemathesis.from_pytest_fixture("simple_schema")
+
+
+@lazy_schema.parametrize()
+def test_(request, case):
+    request.config.HYPOTHESIS_CASES += 1
+"""
+    )
+    result = testdir.runpytest("-v")
+    # Then the generated test should use these fixtures
+    result.assert_outcomes(failed=1)
+    result.stdout.re_match_lines(
+        [
+            r"test_invalid_fixture.py::test_ FAILED",
+            ".*ValueError: The given schema must be an instance of BaseSchema, got: <class 'int'>",
+            r".*1 failed",
+        ]
+    )