tests: Validate main_binary / cargo_binary

`clap` couldn't be used for command line arguments.  I didn't want to
add it as a dependency for clients, which meant it had to be optional.
The problem is that `main_binary` and `cargo_binary` run with optional
features enabled.

Note: you cannot use `main_binary` or `cargo_binary`
- With `Environment::empty` because the executable can't be found
- In skeptic tests (like the README) because the working dir is changed

Author: epage

Cargo.toml

@@ -12,6 +12,9 @@ categories = ["development-tools::testing"]
 keywords = ["cli", "testing", "assert"]
 build = "build.rs"
 
+[[bin]]
+name = "assert_fixture"
+
 [dependencies]
 colored = "1.5"
 difference = "1.0"

src/bin/assert_fixture.rs

@@ -0,0 +1,31 @@
+#[macro_use]
+extern crate error_chain;
+
+use std::env;
+use std::process;
+
+error_chain! {
+    foreign_links {
+        Env(env::VarError);
+        ParseInt(std::num::ParseIntError);
+    }
+}
+
+fn run() -> Result<()> {
+    if let Ok(text) = env::var("stdout") {
+        println!("{}", text);
+    }
+    if let Ok(text) = env::var("stderr") {
+        eprintln!("{}", text);
+    }
+
+    let code = env::var("exit")
+        .ok()
+        .map(|v| v.parse::<i32>())
+        .map_or(Ok(None), |r| r.map(Some))
+        .chain_err(|| "Invalid exit code")?
+        .unwrap_or(0);
+    process::exit(code);
+}
+
+quick_main!(run);

tests/cargo.rs

@@ -0,0 +1,19 @@
+extern crate assert_cli;
+
+#[test]
+fn main_binary() {
+    assert_cli::Assert::main_binary()
+        .with_env(assert_cli::Environment::inherit().insert("stdout", "42"))
+        .stdout()
+        .contains("42")
+        .unwrap();
+}
+
+#[test]
+fn cargo_binary() {
+    assert_cli::Assert::cargo_binary("assert_fixture")
+        .with_env(assert_cli::Environment::inherit().insert("stdout", "42"))
+        .stdout()
+        .contains("42")
+        .unwrap();
+}