add couple of tests for Provides

Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

test.py

@@ -0,0 +1,64 @@
+import os
+import shutil
+import subprocess
+import sys
+import tempfile
+import textwrap
+
+import pytest
+
+DUMMY_LIB = """
+pub fn say_hello() {
+    println!("Hello, World!");
+}
+"""
+DEPGEN = os.path.join(os.path.dirname(__file__), "cargo-deps.py")
+
+
+@pytest.fixture
+def cargo_toml(request):
+    def make_cargo_toml(contents):
+        toml = os.path.join(tmpdir, "Cargo.toml")
+        with open(toml, "w") as fobj:
+            fobj.write(textwrap.dedent(contents))
+        return toml
+
+    tmpdir = tempfile.mkdtemp(prefix="cargo-deps-")
+    srcdir = os.path.join(tmpdir, "src")
+    os.mkdir(srcdir)
+    with open(os.path.join(srcdir, "lib.rs"), "w") as fobj:
+        fobj.write(DUMMY_LIB)
+
+    def finalize():
+        shutil.rmtree(tmpdir)
+    request.addfinalizer(finalize)
+
+    return make_cargo_toml
+
+
+def run(*params):
+    cmd = [sys.executable, DEPGEN, *params]
+    out = subprocess.check_output(cmd, universal_newlines=True)
+    return out.split("\n")[:-1]
+
+
+@pytest.mark.parametrize("toml,expected", [
+    ("""
+     [package]
+     name = "hello"
+     version = "0.0.0"
+     """,
+     ["crate(hello) = 0.0.0"]),
+    ("""
+     [package]
+     name = "hello"
+     version = "1.2.3"
+
+     [features]
+     color = []
+     """,
+     ["crate(hello) = 1.2.3",
+      "crate(hello/color) = 1.2.3"]),
+])
+def test_provides(toml, expected, cargo_toml):
+    assert run("--provides", cargo_toml(toml)) == expected