coverage: Migrate tests/run-coverage into tests/coverage

tests/coverage/if_else.rs

@@ -0,0 +1,40 @@
+#![allow(unused_assignments, unused_variables)]
+
+fn main() {
+    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+    // dependent conditions.
+    let is_true = std::env::args().len() == 1;
+
+    let mut countdown = 0;
+    if
+        is_true
+    {
+        countdown
+        =
+            10
+        ;
+    }
+    else // Note coverage region difference without semicolon
+    {
+        countdown
+        =
+            100
+    }
+
+    if
+        is_true
+    {
+        countdown
+        =
+            10
+        ;
+    }
+    else
+    {
+        countdown
+        =
+            100
+        ;
+    }
+}