doc: highlight --doc only applied on lib target

Author: weihanglo

src/doc/man/cargo-test.md

@@ -38,9 +38,9 @@ manifest settings, in which case your code will need to provide its own `main`
 function to handle running tests.
 
 Documentation tests are also run by default, which is handled by `rustdoc`. It
-extracts code samples from documentation comments and executes them. See the
-[rustdoc book](https://doc.rust-lang.org/rustdoc/) for more information on
-writing doc tests.
+extracts code samples from documentation comments of the library target, and
+then executes them. See the [rustdoc book](https://doc.rust-lang.org/rustdoc/)
+for more information on writing doc tests.
 
 ## OPTIONS
 

src/doc/man/generated_txt/cargo-test.txt

@@ -34,9 +34,10 @@ DESCRIPTION
        its own main function to handle running tests.
 
        Documentation tests are also run by default, which is handled by
-       rustdoc. It extracts code samples from documentation comments and
-       executes them. See the rustdoc book <https://doc.rust-lang.org/rustdoc/>
-       for more information on writing doc tests.
+       rustdoc. It extracts code samples from documentation comments of the
+       library target, and then executes them. See the rustdoc book
+       <https://doc.rust-lang.org/rustdoc/> for more information on writing doc
+       tests.
 
 OPTIONS
    Test Options

src/doc/src/commands/cargo-test.md

@@ -38,9 +38,9 @@ manifest settings, in which case your code will need to provide its own `main`
 function to handle running tests.
 
 Documentation tests are also run by default, which is handled by `rustdoc`. It
-extracts code samples from documentation comments and executes them. See the
-[rustdoc book](https://doc.rust-lang.org/rustdoc/) for more information on
-writing doc tests.
+extracts code samples from documentation comments of the library target, and
+then executes them. See the [rustdoc book](https://doc.rust-lang.org/rustdoc/)
+for more information on writing doc tests.
 
 ## OPTIONS
 

src/etc/man/cargo-test.1

@@ -38,9 +38,9 @@ manifest settings, in which case your code will need to provide its own \fBmain\
 function to handle running tests.
 .sp
 Documentation tests are also run by default, which is handled by \fBrustdoc\fR\&. It
-extracts code samples from documentation comments and executes them. See the
-\fIrustdoc book\fR <https://doc.rust\-lang.org/rustdoc/> for more information on
-writing doc tests.
+extracts code samples from documentation comments of the library target, and
+then executes them. See the \fIrustdoc book\fR <https://doc.rust\-lang.org/rustdoc/>
+for more information on writing doc tests.
 .SH "OPTIONS"
 .SS "Test Options"
 .sp