Expand Env test to check that separate tests are written for multiple…

… Envs (#1157)

### What
Expand Env test to check that separate tests are written for multiple
Envs.

### Why
We don't have a test that checks that multiple files get written in
tests with multiple unique Envs.

Close #1156 

### Merging

Intended to be merged to `main` after:
- #1153

soroban-sdk/src/tests/env.rs

@@ -108,24 +108,42 @@ fn register_contract_deploys_predictable_contract_ids() {
 /// Test that the test snapshot file is written.
 #[test]
 fn test_snapshot_file() {
-    let path = std::path::Path::new("test_snapshots")
+    let p = std::path::Path::new("test_snapshots")
         .join("tests")
         .join("env")
-        .join("test_snapshot_file")
-        .with_extension("1.json");
-    assert!(!path.exists());
+        .join("test_snapshot_file");
+    let p1 = p.with_extension("1.json");
+    let p2 = p.with_extension("2.json");
+    assert!(!p1.exists());
+    assert!(!p2.exists());
     {
         let e1 = Env::default();
-        assert!(!path.exists());
+        assert!(!p1.exists());
+        assert!(!p2.exists());
         let e2 = e1.clone();
-        assert!(!path.exists());
+        assert!(!p1.exists());
+        assert!(!p2.exists());
+        {
+            let _ = Env::default(); // When dropped won't be written because empty.
+        } // Env dropped, nothing written.
+        assert!(!p1.exists());
+        assert!(!p2.exists());
+        {
+            let e3 = Env::default(); // When dropped will be written to p1.
+            let _ = e3.register_contract(None, Contract);
+        } // Env dropped, written to p1.
         let c = e1.register_contract(None, Contract);
-        assert!(!path.exists());
+        assert!(p1.exists());
+        assert!(!p2.exists());
         e1.as_contract(&c, || {});
-        assert!(!path.exists());
+        assert!(p1.exists());
+        assert!(!p2.exists());
         e2.as_contract(&c, || {});
-        assert!(!path.exists());
-    }
-    assert!(path.exists());
-    let _ = std::fs::remove_file(&path);
+        assert!(p1.exists());
+        assert!(!p2.exists());
+    } // Env dropped, written to p2.
+    assert!(p1.exists());
+    assert!(p2.exists());
+    let _ = std::fs::remove_file(&p1);
+    let _ = std::fs::remove_file(&p2);
 }