Tidy tests a bit. (#6122)

substrate/frame/contracts/fixtures/drain.wat

@@ -0,0 +1,54 @@
+(module
+	(import "env" "ext_scratch_size" (func $ext_scratch_size (result i32)))
+	(import "env" "ext_scratch_read" (func $ext_scratch_read (param i32 i32 i32)))
+	(import "env" "ext_balance" (func $ext_balance))
+	(import "env" "ext_call" (func $ext_call (param i32 i32 i64 i32 i32 i32 i32) (result i32)))
+	(import "env" "memory" (memory 1 1))
+
+	(func $assert (param i32)
+		(block $ok
+			(br_if $ok
+				(get_local 0)
+			)
+			(unreachable)
+		)
+	)
+
+	(func (export "deploy"))
+
+	(func (export "call")
+		;; Send entire remaining balance to the 0 address.
+		(call $ext_balance)
+
+		;; Balance should be encoded as a u64.
+		(call $assert
+			(i32.eq
+				(call $ext_scratch_size)
+				(i32.const 8)
+			)
+		)
+
+		;; Read balance into memory.
+		(call $ext_scratch_read
+			(i32.const 8)	;; Pointer to write balance to
+			(i32.const 0)	;; Offset into scratch buffer
+			(i32.const 8)	;; Length of encoded balance
+		)
+
+		;; Self-destruct by sending full balance to the 0 address.
+		(call $assert
+			(i32.eq
+				(call $ext_call
+					(i32.const 0)	;; Pointer to destination address
+					(i32.const 8)	;; Length of destination address
+					(i64.const 0)	;; How much gas to devote for the execution. 0 = all.
+					(i32.const 8)	;; Pointer to the buffer with value to transfer
+					(i32.const 8)	;; Length of the buffer with value to transfer
+					(i32.const 0)	;; Pointer to input data buffer address
+					(i32.const 0)	;; Length of input data buffer
+				)
+				(i32.const 0)
+			)
+		)
+	)
+)