diff --git a/tests/ui/op-assign-builtins-by-ref.rs b/tests/ui/binop/compound-assign-by-ref.rs
similarity index 90%
rename from tests/ui/op-assign-builtins-by-ref.rs
rename to tests/ui/binop/compound-assign-by-ref.rs
index 73788da92321c..e1f519a137fc9 100644
--- a/tests/ui/op-assign-builtins-by-ref.rs
+++ b/tests/ui/binop/compound-assign-by-ref.rs
@@ -1,9 +1,8 @@
+//! Test compound assignment operators with reference right-hand side.
+
 //@ run-pass
 
 fn main() {
-    // test compound assignment operators with ref as right-hand side,
-    // for each operator, with various types as operands.
-
     // test AddAssign
     {
         let mut x = 3i8;
diff --git a/tests/ui/once-cant-call-twice-on-heap.rs b/tests/ui/closures/fnonce-call-twice-error.rs
similarity index 53%
rename from tests/ui/once-cant-call-twice-on-heap.rs
rename to tests/ui/closures/fnonce-call-twice-error.rs
index 3fd8c5cadca98..1662b7bddaaee 100644
--- a/tests/ui/once-cant-call-twice-on-heap.rs
+++ b/tests/ui/closures/fnonce-call-twice-error.rs
@@ -1,16 +1,15 @@
-// Testing guarantees provided by once functions.
-// This program would segfault if it were legal.
+//! Test that `FnOnce` closures cannot be called twice.
 
 use std::sync::Arc;
 
-fn foo<F:FnOnce()>(blk: F) {
+fn foo<F: FnOnce()>(blk: F) {
     blk();
     blk(); //~ ERROR use of moved value
 }
 
 fn main() {
     let x = Arc::new(true);
-    foo(move|| {
+    foo(move || {
         assert!(*x);
         drop(x);
     });
diff --git a/tests/ui/once-cant-call-twice-on-heap.stderr b/tests/ui/closures/fnonce-call-twice-error.stderr
similarity index 56%
rename from tests/ui/once-cant-call-twice-on-heap.stderr
rename to tests/ui/closures/fnonce-call-twice-error.stderr
index 42697374115ca..51d8a33dcd796 100644
--- a/tests/ui/once-cant-call-twice-on-heap.stderr
+++ b/tests/ui/closures/fnonce-call-twice-error.stderr
@@ -1,18 +1,18 @@
 error[E0382]: use of moved value: `blk`
-  --> $DIR/once-cant-call-twice-on-heap.rs:8:5
+  --> $DIR/fnonce-call-twice-error.rs:7:5
    |
-LL | fn foo<F:FnOnce()>(blk: F) {
-   |                    --- move occurs because `blk` has type `F`, which does not implement the `Copy` trait
+LL | fn foo<F: FnOnce()>(blk: F) {
+   |                     --- move occurs because `blk` has type `F`, which does not implement the `Copy` trait
 LL |     blk();
    |     ----- `blk` moved due to this call
 LL |     blk();
    |     ^^^ value used here after move
    |
 note: `FnOnce` closures can only be called once
-  --> $DIR/once-cant-call-twice-on-heap.rs:6:10
+  --> $DIR/fnonce-call-twice-error.rs:5:11
    |
-LL | fn foo<F:FnOnce()>(blk: F) {
-   |          ^^^^^^^^ `F` is made to be an `FnOnce` closure here
+LL | fn foo<F: FnOnce()>(blk: F) {
+   |           ^^^^^^^^ `F` is made to be an `FnOnce` closure here
 LL |     blk();
    |     ----- this value implements `FnOnce`, which causes it to be moved when called
 
diff --git a/tests/ui/occurs-check-2.rs b/tests/ui/occurs-check-2.rs
deleted file mode 100644
index 9289a8e870a18..0000000000000
--- a/tests/ui/occurs-check-2.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-fn main() {
-
-    let f;
-    let g;
-
-    g = f;
-    //~^ ERROR overflow assigning `Box<_>` to `_`
-    f = Box::new(g);
-}
diff --git a/tests/ui/occurs-check-3.rs b/tests/ui/occurs-check-3.rs
deleted file mode 100644
index 377a043daf3f6..0000000000000
--- a/tests/ui/occurs-check-3.rs
+++ /dev/null
@@ -1,11 +0,0 @@
-// From Issue #778
-
-enum Clam<T> { A(T) }
-fn main() {
-    let c;
-    c = Clam::A(c);
-    //~^ ERROR overflow assigning `Clam<_>` to `_`
-    match c {
-        Clam::A::<isize>(_) => { }
-    }
-}
diff --git a/tests/ui/occurs-check.rs b/tests/ui/occurs-check.rs
deleted file mode 100644
index 638b9b6d7e4c2..0000000000000
--- a/tests/ui/occurs-check.rs
+++ /dev/null
@@ -1,5 +0,0 @@
-fn main() {
-    let f;
-    f = Box::new(f);
-    //~^ ERROR overflow assigning `Box<_>` to `_`
-}
diff --git a/tests/ui/opeq.rs b/tests/ui/opeq.rs
deleted file mode 100644
index 956ea0684fa70..0000000000000
--- a/tests/ui/opeq.rs
+++ /dev/null
@@ -1,17 +0,0 @@
-//@ run-pass
-
-pub fn main() {
-    let mut x: isize = 1;
-    x *= 2;
-    println!("{}", x);
-    assert_eq!(x, 2);
-    x += 3;
-    println!("{}", x);
-    assert_eq!(x, 5);
-    x *= x;
-    println!("{}", x);
-    assert_eq!(x, 25);
-    x /= 5;
-    println!("{}", x);
-    assert_eq!(x, 5);
-}
diff --git a/tests/ui/oom_unwind.rs b/tests/ui/panics/oom-panic-unwind.rs
similarity index 86%
rename from tests/ui/oom_unwind.rs
rename to tests/ui/panics/oom-panic-unwind.rs
index be5e63d430b70..5974ad91406f3 100644
--- a/tests/ui/oom_unwind.rs
+++ b/tests/ui/panics/oom-panic-unwind.rs
@@ -1,3 +1,5 @@
+//! Test that out-of-memory conditions trigger catchable panics with `-Z oom=panic`.
+
 //@ compile-flags: -Z oom=panic
 //@ run-pass
 //@ no-prefer-dynamic
diff --git a/tests/ui/opt-in-copy.rs b/tests/ui/traits/copy-requires-all-fields-copy.rs
similarity index 82%
rename from tests/ui/opt-in-copy.rs
rename to tests/ui/traits/copy-requires-all-fields-copy.rs
index d0257b5745d8b..8c829a7382b3e 100644
--- a/tests/ui/opt-in-copy.rs
+++ b/tests/ui/traits/copy-requires-all-fields-copy.rs
@@ -1,3 +1,5 @@
+//! Test that `Copy` cannot be implemented if any field doesn't implement `Copy`.
+
 struct CantCopyThis;
 
 struct IWantToCopyThis {
diff --git a/tests/ui/opt-in-copy.stderr b/tests/ui/traits/copy-requires-all-fields-copy.stderr
similarity index 86%
rename from tests/ui/opt-in-copy.stderr
rename to tests/ui/traits/copy-requires-all-fields-copy.stderr
index 258ff16e6e485..1a9e1ada36637 100644
--- a/tests/ui/opt-in-copy.stderr
+++ b/tests/ui/traits/copy-requires-all-fields-copy.stderr
@@ -1,5 +1,5 @@
 error[E0204]: the trait `Copy` cannot be implemented for this type
-  --> $DIR/opt-in-copy.rs:7:15
+  --> $DIR/copy-requires-all-fields-copy.rs:9:15
    |
 LL |     but_i_cant: CantCopyThis,
    |     ------------------------ this field does not implement `Copy`
@@ -8,7 +8,7 @@ LL | impl Copy for IWantToCopyThis {}
    |               ^^^^^^^^^^^^^^^
 
 error[E0204]: the trait `Copy` cannot be implemented for this type
-  --> $DIR/opt-in-copy.rs:19:15
+  --> $DIR/copy-requires-all-fields-copy.rs:21:15
    |
 LL |     ButICant(CantCopyThisEither),
    |              ------------------ this field does not implement `Copy`
diff --git a/tests/ui/type-inference/direct-self-reference-occurs-check.rs b/tests/ui/type-inference/direct-self-reference-occurs-check.rs
new file mode 100644
index 0000000000000..6e3d8251fc4f8
--- /dev/null
+++ b/tests/ui/type-inference/direct-self-reference-occurs-check.rs
@@ -0,0 +1,9 @@
+//! Test that occurs check prevents direct self-reference in variable assignment.
+//!
+//! Regression test for <https://github.com/rust-lang/rust/issues/768>.
+
+fn main() {
+    let f;
+    f = Box::new(f);
+    //~^ ERROR overflow assigning `Box<_>` to `_`
+}
diff --git a/tests/ui/occurs-check.stderr b/tests/ui/type-inference/direct-self-reference-occurs-check.stderr
similarity index 79%
rename from tests/ui/occurs-check.stderr
rename to tests/ui/type-inference/direct-self-reference-occurs-check.stderr
index ea7c541abc135..6c522ffac1f7a 100644
--- a/tests/ui/occurs-check.stderr
+++ b/tests/ui/type-inference/direct-self-reference-occurs-check.stderr
@@ -1,5 +1,5 @@
 error[E0275]: overflow assigning `Box<_>` to `_`
-  --> $DIR/occurs-check.rs:3:18
+  --> $DIR/direct-self-reference-occurs-check.rs:7:18
    |
 LL |     f = Box::new(f);
    |                  ^
diff --git a/tests/ui/type-inference/enum-self-reference-occurs-check.rs b/tests/ui/type-inference/enum-self-reference-occurs-check.rs
new file mode 100644
index 0000000000000..2905868b8bfa9
--- /dev/null
+++ b/tests/ui/type-inference/enum-self-reference-occurs-check.rs
@@ -0,0 +1,16 @@
+//! Test that occurs check prevents infinite types with enum self-references.
+//!
+//! Regression test for <https://github.com/rust-lang/rust/issues/778>.
+
+enum Clam<T> {
+    A(T),
+}
+
+fn main() {
+    let c;
+    c = Clam::A(c);
+    //~^ ERROR overflow assigning `Clam<_>` to `_`
+    match c {
+        Clam::A::<isize>(_) => {}
+    }
+}
diff --git a/tests/ui/occurs-check-3.stderr b/tests/ui/type-inference/enum-self-reference-occurs-check.stderr
similarity index 80%
rename from tests/ui/occurs-check-3.stderr
rename to tests/ui/type-inference/enum-self-reference-occurs-check.stderr
index eb05c94957c98..3239be51a1766 100644
--- a/tests/ui/occurs-check-3.stderr
+++ b/tests/ui/type-inference/enum-self-reference-occurs-check.stderr
@@ -1,5 +1,5 @@
 error[E0275]: overflow assigning `Clam<_>` to `_`
-  --> $DIR/occurs-check-3.rs:6:17
+  --> $DIR/enum-self-reference-occurs-check.rs:11:17
    |
 LL |     c = Clam::A(c);
    |                 ^
diff --git a/tests/ui/type-inference/infinite-type-occurs-check.rs b/tests/ui/type-inference/infinite-type-occurs-check.rs
new file mode 100644
index 0000000000000..b353824e931d4
--- /dev/null
+++ b/tests/ui/type-inference/infinite-type-occurs-check.rs
@@ -0,0 +1,12 @@
+//! Test that occurs check prevents infinite types during type inference.
+//!
+//! Regression test for <https://github.com/rust-lang/rust/issues/768>.
+
+fn main() {
+    let f;
+    let g;
+
+    g = f;
+    //~^ ERROR overflow assigning `Box<_>` to `_`
+    f = Box::new(g);
+}
diff --git a/tests/ui/occurs-check-2.stderr b/tests/ui/type-inference/infinite-type-occurs-check.stderr
similarity index 81%
rename from tests/ui/occurs-check-2.stderr
rename to tests/ui/type-inference/infinite-type-occurs-check.stderr
index 5f296967f30d8..9cb8bb917962e 100644
--- a/tests/ui/occurs-check-2.stderr
+++ b/tests/ui/type-inference/infinite-type-occurs-check.stderr
@@ -1,5 +1,5 @@
 error[E0275]: overflow assigning `Box<_>` to `_`
-  --> $DIR/occurs-check-2.rs:6:9
+  --> $DIR/infinite-type-occurs-check.rs:9:9
    |
 LL |     g = f;
    |         ^