fix issue with test_requires and components

conans/model/build_info.py

@@ -553,11 +553,13 @@ def check_component_requires(self, conanfile):
         # Only direct host dependencies can be used with components
         direct_dependencies = [d.ref.name
                                for d, _ in conanfile.dependencies.filter({"direct": True,
-                                                                          "build": False}).items()]
+                                                                          "build": False,
+                                                                          "test": False}).items()]
         for e in external:
             if e not in direct_dependencies:
                 raise ConanException(
                     f"{conanfile}: required component package '{e}::' not in dependencies")
+        # TODO: discuss if there are cases that something is required but not transitive
         for e in direct_dependencies:
             if e not in external:
                 raise ConanException(

conans/test/integration/graph/test_test_requires.py

@@ -117,3 +117,33 @@ def build_requirements(self):
     assert "gtest/1.0: MYOPTION: 2" in c.out
     c.run("create engine -o gtest*:myoption=3")
     assert "gtest/1.0: MYOPTION: 3" in c.out
+
+
+def test_requires_components():
+    """ this test used to fail with "gtest" not required by components
+    It is important to have at least 1 external ``requires`` because with
+    no requires at all it doesn't fail.
+    https://github.com/conan-io/conan/issues/13187
+    """
+    c = TestClient()
+    conanfile = textwrap.dedent("""
+        from conan import ConanFile
+
+        class MyLib(ConanFile):
+            name = "mylib"
+            version = "0.1"
+
+            requires = "openssl/1.1"
+            test_requires = "gtest/1.0"
+
+            def package_info(self):
+                self.cpp_info.components["mylib"].requires = ["openssl::openssl"]
+        """)
+    c.save({"gtest/conanfile.py": GenConanfile("gtest", "1.0"),
+            "openssl/conanfile.py": GenConanfile("openssl", "1.1"),
+            "pkg/conanfile.py": conanfile})
+    c.run("create gtest")
+    c.run("create openssl")
+    c.run("create pkg")
+    # This NO LONGER FAILS
+    c.assert_listed_require({"gtest/1.0": "Cache"}, test=True)