Move test harness to separate package

Cargo.toml

@@ -1,3 +1,4 @@
 [workspace]
+resolver = "2"
 
-members = ["dotenv", "dotenv_codegen"]
+members = ["dotenv", "dotenv_codegen", "test_util"]

dotenv/Cargo.toml

@@ -29,8 +29,8 @@ required-features = ["cli"]
 clap = { version = "4.3.11", optional = true }
 
 [dev-dependencies]
+dotenvy_test_util = { path = "../test_util", version = "0.1.0" }
 tempfile = "3.3.0"
-once_cell = "1.16.0"
 
 [features]
 cli = ["clap"]

dotenv/tests/integration/dotenv.rs

@@ -0,0 +1,23 @@
+use dotenvy_test_util::*;
+
+const TEST_KEY: &str = "TEST_KEY";
+const TEST_VALUE: &str = "test_val";
+const EXISTING_KEY: &str = "EXISTING_KEY";
+const EXISTING_VALUE: &str = "loaded_from_env";
+
+const TEST_ENV_FILE: &str = r"
+TEST_KEY=test_val
+EXISTING_KEY=loaded_from_file
+";
+
+#[test]
+fn dotenv_ok() -> Result<(), Error> {
+    let mut testenv = TestEnv::new()?;
+    testenv.add_env_file(".env", TEST_ENV_FILE)?;
+    testenv.add_env_var(EXISTING_KEY, EXISTING_VALUE)?;
+    test_in_env(&testenv, || {
+        dotenvy::dotenv().ok();
+        assert_env_var(TEST_KEY, TEST_VALUE);
+        assert_env_var(EXISTING_KEY, EXISTING_VALUE);
+    })
+}

dotenv/tests/integration/main.rs

@@ -1 +1 @@
-mod util;
+mod dotenv;