Add a simple testdata tree with missing coverage

Cargo.toml

@@ -98,6 +98,7 @@ exclude = [
     "testdata/tree/hang_when_mutated",
     "testdata/tree/insta",
     "testdata/tree/integration_tests",
+    "testdata/tree/missing_test",
     "testdata/tree/mut_ref",
     "testdata/tree/never_type",
     "testdata/tree/override_dependency",

testdata/tree/missing_test/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "cargo-mutants-testdata-missing-test"
+version = "0.0.0"
+edition = "2018"
+authors = ["Martin Pool"]
+publish = false
+

testdata/tree/missing_test/src/lib.rs

@@ -0,0 +1,8 @@
+fn is_symlink(unix_mode: u32) -> bool {
+    unix_mode & 0o140000 != 0
+}
+
+#[test]
+fn test_symlink() {
+    assert!(is_symlink(0o147777));
+}

tests/cli/snapshots/cli__list_mutants_in_all_trees_as_json.snap

@@ -357,6 +357,31 @@ expression: buf
 ]
 ```
 
+## testdata/tree/missing_test
+
+```json
+[
+  {
+    "package": "cargo-mutants-testdata-missing-test",
+    "file": "src/lib.rs",
+    "line": 1,
+    "function": "is_symlink",
+    "return_type": "-> bool",
+    "replacement": "true",
+    "genre": "FnValue"
+  },
+  {
+    "package": "cargo-mutants-testdata-missing-test",
+    "file": "src/lib.rs",
+    "line": 1,
+    "function": "is_symlink",
+    "return_type": "-> bool",
+    "replacement": "false",
+    "genre": "FnValue"
+  }
+]
+```
+
 ## testdata/tree/mut_ref
 
 ```json

tests/cli/snapshots/cli__list_mutants_in_all_trees_as_text.snap

@@ -105,6 +105,13 @@ src/lib.rs:1: replace double -> u32 with 0
 src/lib.rs:1: replace double -> u32 with 1
 ```
 
+## testdata/tree/missing_test
+
+```
+src/lib.rs:1: replace is_symlink -> bool with true
+src/lib.rs:1: replace is_symlink -> bool with false
+```
+
 ## testdata/tree/mut_ref
 
 ```