Try to determine the path of PostgreSQL server commands from pg_config

pg_config is usually in the path of many distros, as soon as postgresql-client tools are installed, but server commands are not.
That's why we always had to adjust the PATH accordingly.
Determining the path of these commands automatically makes testing easier.

Extracted from #1

README.md

@@ -214,21 +214,22 @@ After checking out the source, install all dependencies:
 
     $ bundle install
 
-Cleanup extension files, packaging files, test databases:
+Cleanup extension files, packaging files, test databases.
+Run this to change between PostgreSQL versions:
 
     $ rake clean
 
 Compile extension:
 
     $ rake compile
 
-Run tests/specs with PostgreSQL tools like `initdb` in the path:
+Run tests/specs on the PostgreSQL version that `pg_config --bindir` points to:
 
-    $ PATH=$PATH:/usr/lib/postgresql/14/bin rake test
+    $ rake test
 
-Or run a specific test with the line number:
+Or run a specific test per file and line number on a specific PostgreSQL version:
 
-    $ PATH=$PATH:/usr/lib/postgresql/14/bin rspec -Ilib -fd spec/pg/connection_spec.rb:455
+    $ PATH=/usr/lib/postgresql/14/bin:$PATH rspec -Ilib -fd spec/pg/connection_spec.rb:455
 
 Generate the API documentation:
 

spec/helpers.rb

@@ -252,6 +252,7 @@ def initialize( name, port: 54321, postgresql_conf: '' )
 			@test_dir = TEST_DIRECTORY + "tmp_test_#{@name}"
 			@test_pgdata = @test_dir + 'data'
 			@test_pgdata.mkpath
+			@pg_bin_dir = nil
 
 			@logfile = @test_dir + 'setup.log'
 			trace "Command output logged to #{@logfile}"
@@ -260,7 +261,7 @@ def initialize( name, port: 54321, postgresql_conf: '' )
 				unless (@test_pgdata+"postgresql.conf").exist?
 					FileUtils.rm_rf( @test_pgdata, :verbose => $DEBUG )
 					trace "Running initdb"
-					log_and_run @logfile, 'initdb', '-E', 'UTF8', '--no-locale', '-D', @test_pgdata.to_s
+					log_and_run @logfile, pg_bin_path('initdb'), '-E', 'UTF8', '--no-locale', '-D', @test_pgdata.to_s
 				end
 
 				unless (@test_pgdata+"ruby-pg-server-cert").exist?
@@ -293,7 +294,7 @@ def initialize( name, port: 54321, postgresql_conf: '' )
 				trace "Starting postgres"
 				sopt = "-p #{@port}"
 				sopt += " -k #{@test_dir.to_s.dump}" unless RUBY_PLATFORM=~/mingw|mswin/i
-				log_and_run @logfile, 'pg_ctl', '-w', '-o', sopt,
+				log_and_run @logfile, pg_bin_path('pg_ctl'), '-w', '-o', sopt,
 					'-D', @test_pgdata.to_s, 'start'
 				sleep 2
 
@@ -328,8 +329,8 @@ def generate_ssl_certs(output_dir)
 
 		def create_test_db
 			trace "Creating the test DB"
-			log_and_run @logfile, 'psql', '-p', @port.to_s, '-e', '-c', 'DROP DATABASE IF EXISTS test', 'postgres'
-			log_and_run @logfile, 'createdb', '-p', @port.to_s, '-e', 'test'
+			log_and_run @logfile, pg_bin_path('psql'), '-p', @port.to_s, '-e', '-c', 'DROP DATABASE IF EXISTS test', 'postgres'
+			log_and_run @logfile, pg_bin_path('createdb'), '-p', @port.to_s, '-e', 'test'
 		end
 
 		def connect
@@ -344,7 +345,16 @@ def connect
 		def teardown
 			trace "Tearing down test database for #{@name}"
 
-			log_and_run @logfile, 'pg_ctl', '-D', @test_pgdata.to_s, 'stop'
+			log_and_run @logfile, pg_bin_path('pg_ctl'), '-D', @test_pgdata.to_s, 'stop'
+		end
+
+		def pg_bin_path(cmd)
+			@pg_bin_dir ||= begin
+				`pg_config --bindir`.strip
+			rescue
+				nil
+			end
+			[@pg_bin_dir&.empty? ? nil : @pg_bin_dir, cmd].compact.join("/")
 		end
 	end